Map of Menai Strait [Ordnance Survey]
So long as the dangerous
Straits of Menai had to be crossed in an open ferry-boat, the communication
between London and Holyhead was necessarily considered incomplete. While the
roads through North Wales were so dangerous as to deter travellers between
England and Ireland from using that route, the completion of the remaining
link of communication across the Straits was of comparatively little
importance. But when those roads had, by the application of much capital,
skill, and labour, been rendered so safe and convenient that the mail and
stage coaches could run over them at the rate of from eight to ten miles an
hour, the bridging of the Straits became a measure of urgent public
necessity. The increased traffic by this route so much increased the
quantity of passengers and luggage, that the open boats were often
dangerously overloaded; and serious accidents, attended with loss of life
and property, came to be of frequent occurrence.
The erection of a bridge over
the Straits had long been matter of speculation amongst engineers. As early
as 1776, Mr. Golborne proposed his plan of an embankment with a bridge in
the middle of it; and a few years later, in 1785, Mr. Nichols proposed a
wooden viaduct, furnished with drawbridges at Cadnant Island. Later still,
Mr. Rennie proposed his design of a cast iron bridge. But none of these
plans were carried out, and the whole subject remained in abeyance until the
year 1810, when a commission was appointed to inquire and report as to the
state of the roads between Shrewsbury, Chester, and Holyhead. The result
was, that Mr. Telford was called upon to report as to the most effectual
method of bridging the Menai Strait, and thus completing the communication
with the port of embarkation for Ireland.
Telford's proposed Cast Iron Bridge
Mr. Telford submitted
alternative plans for a bridge over the Strait: one at the Swilly Rock,
consisting of three cast iron arches of 260 feet span, with a stone arch of
100 feet span between each two iron ones, to resist their lateral thrust;
and another at Ynys-y-moch, to which he himself attached the preference,
consisting of a single cast iron arch of 500 feet span, the crown of the
arch to be 100 feet above high water of spring tides, and the breadth of the
roadway to be 40 feet.
The principal objection taken
to this plan by engineers generally, was the supposed difficulty of erecting
a proper centering to support the arch during construction; and the mode by
which Mr. Telford proposed to overcome this may be cited in illustration of
his ready ingenuity in overcoming difficulties. He proposed to suspend the
centering from above instead of supporting it from below in the usual
manner--a contrivance afterwards revived by another very skilful engineer,
the late Mr. Brunel. Frames, 50 feet high, were to be erected on the top of
the abutments, and on these, strong blocks, or rollers and chains, were to
be fixed, by means of which, and by the aid of windlasses and other
mechanical powers, each separate piece of centering was to be raised into,
and suspended in, its proper place. Mr. Telford regarded this method of
constructing centres as applicable to stone as well as to iron arches; and
indeed it is applicable, as Mr. Brunel held, to the building of the arch
itself.*[1]
Proposed Plan of Suspended Centering
Mr. Telford anticipated that,
if the method recommended by him were successfully adopted on the large
scale proposed at Menai, all difficulties with regard to carrying bridges
over deep ravines would be done away with, and a new era in bridge-building
begun. For this and other reasons--but chiefly because of the much greater
durability of a cast iron bridge compared with the suspension bridge
afterwards adopted--it is matter of regret that he was not permitted to
carry out this novel and grand design. It was, however, again objected by
mariners that the bridge would seriously affect, if not destroy, the
navigation of the Strait; and this plan, like Mr. Rennie's, was eventually
rejected.
Several years passed, and
during the interval Mr. Telford was consulted as to the construction of a
bridge over Runcorn Gap on the Mersey, above Liverpool. As the river was
there about 1200 feet wide, and much used for purposes of navigation, a
bridge of the ordinary construction was found inapplicable. But as he was
required to furnish a plan of the most suitable structure, he proceeded to
consider how the difficulties of the case were to be met. The only
practicable plan, he thought, was a bridge constructed on the principle of
suspension. Expedients of this kind had long been employed in India and
America, where wide rivers were crossed by means of bridges formed of ropes
and chains; and even in this country a suspension bridge, though of a very
rude kind, had long been in use near Middleton on the Tees, where, by means
of two common chains stretched across the river, upon which a footway of
boards was laid, the colliers were enabled to pass from their cottages to
the colliery on the opposite bank.
Captain (afterwards Sir
Samuel) Brown took out a patent for forming suspension bridges in 1817; but
it appears that Telford's attention had been directed to the subject before
this time, as he was first consulted respecting the Runcorn Bridge in the
year 1814, when he proceeded to make an elaborate series of experiments on
the tenacity of wrought iron bars, with the object of employing this
material in his proposed structure. After he had made upwards of two hundred
tests of malleable iron of various qualities, he proceeded to prepare his
design of a bridge, which consisted of a central opening of 1000 feet span,
and two side openings of 500 feet each, supported by pyramids of masonry
placed near the low-water lines. The roadway was to be 30 feet wide, divided
into one central footway and two distinct carriageways of 12 feet each. At
the same time he prepared and submitted a model of the central opening,
which satisfactorily stood the various strains which were applied to it.
This Runcorn design of 1814 was of a very magnificent character, perhaps
superior even to that of the Menai Suspension Bridge, afterwards erected;
but unhappily the means were not forthcoming to carry it into effect. The
publication of his plan and report had, however, the effect of directing
public attention to the construction of bridges on the suspension principle;
and many were shortly after designed and erected by Telford and other
engineers in different parts of the kingdom.
Mr. Telford continued to be
consulted by the Commissioners of the Holyhead Roads as to the completion of
the last and most important link in the line of communication between London
and Holyhead, by bridging the Straits of Menai; and at one of their meetings
in 1815, shortly after the publication of his Runcorn design, the inquiry
was made whether a bridge upon the same principle was not applicable in this
particular case. The engineer was instructed again to examine the Straits
and submit a suitable plan and estimate, which he proceeded to do in the
early part of 1818. The site selected by him as the most favourable was that
which had been previously fixed upon for the projected cast iron bridge,
namely at Ynys-y-moch--the shores there being bold and rocky, affording easy
access and excellent foundations, while by spanning the entire channel
between the low-water lines, and the roadway being kept uniformly 100 feet
above the highest water at spring tide, the whole of the navigable waterway
would be left entirely uninterrupted. The distance between the centres of
the supporting pyramids was proposed to be of the then unprecedented width
of 550 feet, and the height of the pyramids 53 feet above the level of the
roadway. The main chains were to be sixteen in number, with a deflection of
37 feet, each composed of thirty-six bars of half-inch-square iron, so
placed as to give a square of six on each side, making the whole chain about
four inches in diameter, welded together for their whole length, secured by
bucklings, and braced round with iron wire; while the ends of these great
chains were to be secured by a mass of masonry built over stone arches
between each end of the supporting piers and the adjoining shore. Four of
the arches were to be on the Anglesea, and three on the Caernarvonshire
side, each of them of 52 feet 6 inches span. The roadway was to be divided,
as in the Runcorn design with a carriage way 12 feet wide on each side, and
a footpath of 4 feet in the middle. Mr. Telford's plan was supported by Mr.
Rennie and other engineers of eminence; and the Select Committee of the
House of Commons, being satisfied as to its practicability, recommended
Parliament to pass a Bill and to make a grant of money to enable the work to
be carried into effect.
Outline of Menai Bridge
The necessary Act passed in
the session of 1819, and Mr. Telford immediately proceeded to Bangor to make
preparations for beginning the works. The first proceeding was to blast off
the inequalities of the surface of the rock called Ynys-y-moch, situated on
the western or Holyhead side of the Strait, at that time accessible only at
low water. The object was to form an even surface upon it for the foundation
of the west main pier. It used to be at this point, where the Strait was
narrowest, that horned cattle were driven down, preparatory to swimming them
across the channel to the Caernarvon side, when the tide was weak and at its
lowest ebb. The cattle were, nevertheless, often carried away, the current
being too strong for the animals to contend against it.
At the same time, a
landing-quay was erected on Ynys-y-moch, which was connected with the shore
by an embankment carrying lines of railway. Along these, horses drew the
sledges laden with stone required for the work; the material being brought
in barges from the quarries opened at Penmon Point, on the north-eastern
extremity of the Isle of Anglesea, a little to the westward of the northern
opening of the Strait. When the surface of the rock had been levelled and
the causeway completed, the first stone of the main pier was laid by Mr. W.A.
Provis, the resident engineer, on the 10th of August, 1819; but not the
slightest ceremony was observed on the occasion.
Later in the autumn,
preparations were made for proceeding with the foundations of the eastern
main pier on the Bangor side of the Strait. After excavating the beach to a
depth of 7 feet, a solid mass of rock was reached, which served the purpose
of an immoveable foundation for the pier. At the same, time workshops were
erected; builders, artisans, and labourers were brought together from
distant quarters; vessels and barges were purchased or built for the special
purpose of the work; a quay was constructed at Penmon Point for loading the
stones for the piers; and all the requisite preliminary arrangements were
made for proceeding with the building operations in the ensuing spring.
A careful specification of
the masonry work was drawn up, and the contract was let to Messrs. Stapleton
and Hall; but as they did not proceed satisfactorily, and desired to be
released from the contract, it was relet on the same terms to Mr. John
Wilson, one of Mr. Telford's principal contractors for mason work on the
Caledonian Canal. The building operations were begun with great vigour early
in 1820. The three arches on the Caernarvonshire side and the four on the
Anglesea side were first proceeded with. They are of immense magnitude, and
occupied four years in construction, having been finished late in the autumn
of 1824. These piers are 65 feet in height from high-water line to the
springing of the arches, the span of each being 52 feet 6 inches. The work
of the main piers also made satisfactory progress, and the masonry proceeded
so rapidly that stones could scarcely be got from the quarries in sufficient
quantity to keep the builders at work. By the end of June about three
hundred men were employed.
The two principal piers, each
153 feet in height, upon which the main chains of the bridge were to be
suspended, were built with great care and under rigorous inspection. In
these, as indeed in most of the masonry of the bridge, Mr. Telford adopted
the same practice which he had employed in his previous bridge structures,
that of leaving large void spaces, commencing above high water mark and
continuing them up perpendicularly nearly to the level of the roadway. "I
have elsewhere expressed my conviction," he says, when referring to the mode
of constructing these piers, "that one of the most important improvements
which I have been able to introduce into masonry consists in the preference
of cross-walls to rubble, in the structure of a pier, or any other edifice
requiring strength. Every stone and joint in such walls is open to
inspection in the progress of the work, and even afterwards, if necessary;
but a solid filling of rubble conceals itself, and may be little better than
a heap of rubbish confined by side walls." The walls of these main piers
were built from within as well as from without all the way up, and the
inside was as carefully and closely cemented with mortar as the external
face. Thus the whole pier was bound firmly together, and the utmost strength
given, while the weight of the superstructure upon the lower parts of the
work was reduced to its minimum.
Section of Main Pier
Over the main piers, the
small arches intended for the roadways were constructed, each being 15 feet
to the springing of the arch, and 9 feet wide. Upon these arches the masonry
was carried upwards, in a tapering form, to a height of 53 feet above the
level of the road. As these piers were to carry the immense weight of the
suspension chains, great pains were taken with their construction, and all
the stones, from top to bottom, were firmly bound together with iron dowels
to prevent the possibility of their being separated or bulged by the immense
pressure they had to withstand.
The most important point in
the execution of the details of the bridge, where the engineer had no past
experience to guide him, was in the designing and fixing of the wrought iron
work. Mr. Telford had continued his experiments as to the tenacity of bar
iron, until he had obtained several hundred distinct tests; and at length,
after the most mature delilberation, the patterns and dimensions were
finally arranged by him, and the contract for the manufacture of the whole
was let to Mr. Hazeldean, of Shrewsbury, in the year 1820. The iron was to
be of the best Shropshire, drawn at Upton forge, and finished and proved at
the works, under the inspection of a person appointed by the engineer.
Cut showing fixing of the chains in the rock
The mode by which the land
ends of these enormous suspension chains were rooted to the solid ground on
either side of the Strait, was remarkably ingenious and effective. Three
oblique tunnels were made by blasting the rock on the Anglesea side; they
were each about six feet in diameter, the excavations being carried down an
inclined plane to the depth of about twenty yards. A considerable width of
rock lay between each tunnel, but at the bottom they were all united by a
connecting horizontal avenue or cavern, sufficiently capacious to enable the
workmen to fix the strong iron frames, composed principally of thick flat
cast iron plates, which were engrafted deeply into the rock, and strongly
bound together by the iron work passing along the horizontal avenue; so
that, if the iron held, the chains could only yield by tearing up the whole
mass of solid rock under which they were thus firmly bound.
A similar method of anchoring
the main chains was adopted on the Caernarvonshire side. A thick bank of
earth had there to be cut through, and a solid mass of masonry built in its
place, the rock being situated at a greater distance from the main pier;
involving a greater length of suspending chain, and a disproportion in the
catenary or chord line on that side of the bridge. The excavation and
masonry thereby rendered necessary proved a work of vast labour, and its
execution occupied a considerable time; but by the beginning of the year
1825 the suspension pyramids, the land piers and arches, and the rock
tunnels, had all been completed, and the main chains were firmly secured in
them; the work being sufficiently advanced to enable the suspending of the
chains to be proceeded with. This was by far the most difficult and anxious
part of the undertaking.
With the same careful
forethought and provision for every contingency which had distinguished the
engineer's procedure in the course of the work, he had made frequent
experiments to ascertain the actual power which would be required to raise
the main chains to their proper curvature. A valley lay convenient for the
purpose, a little to the west of the bridge on the Anglesea side.
Fifty-seven of the intended vertical suspending rods, each nearly ten feet
long and an inch square, having been fastened together, a piece of chain was
attached to one end to make the chord line 570 feet in length; and
experiments having been made and comparisons drawn, Mr. Telford ascertained
that the absolute weight of one of the main chains of the bridge between the
points of suspension was 23 1/2 tons, requiring a strain of 39 1/2 tons to
raise it to its proper curvature. On this calculation the necessary
apparatus required for the hoisting was prepared. The mode of action finally
determined on for lifting the main chains, and fixing them into their
places, was to build the central portion of each upon a raft 450 feet long
and 6 feet wide, then to float it to the site of the bridge, and lift it
into its place by capstans and proper tackle.
At length all was ready for
hoisting the first great chain, and about the middle of April, 1825, Mr.
Telford left London for Bangor to superintend the operations. An immense
assemblage collected to witness the sight; greater in number than any that
had been collected in the same place since the men of Anglesea, in their
war-paint, rushing down to the beach, had shrieked defiance across the
Straits at their Roman invaders on the Caernarvon shore. Numerous boats
arrayed in gay colours glided along the waters; the day--the 26th of
April--being bright, calm, and in every way propitious.
At half-past two, about an
hour before high water, the raft bearing the main chain was cast off from
near Treborth Mill, on the Caernarvon side. Towed by four boats, it began
gradually to move from the shore, and with the assistance of the tide, which
caught it at its further end, it swung slowly and majestically round to its
position between the main piers, where it was moored. One end of the chain
was then bolted to that which hung down the face of the Caernarvon pier;
whilst the other was attached to ropes connected with strong capstans fixed
on the Anglesea side, the ropes passing by means of blocks over the top of
the pyramid of the Anglesea pier. The capstans for hauling in the ropes
bearing the main chain, were two in number, manned by about 150 labourers.
When all was ready, the signal was given to "Go along!" A Band of fifers
struck up a lively tune; the capstans were instantly in motion, and the men
stepped round in a steady trot. All went well. The ropes gradually coiled
in. As the strain increased, the pace slackened a little; but "Heave away,
now she comes!" was sung out. Round went the men, and steadily and safely
rose the ponderous chain.
Cut of Bridge, showing state of Suspension Chain
The tide had by this time
turned, and bearing upon the side of the raft, now getting freer of its
load, the current floated it away from under the middle of the chain still
resting on it, and it swung easily off into the water. Until this moment a
breath less silence pervaded the watching multitude; and nothing was heard
among the working party on the Anglesea side but the steady tramp of the men
at the capstans, the shrill music of the fife, and the occasional order to
"Hold on!" or "Go along!" But no sooner was the raft seen floating away, and
the great chain safely swinging in the air, than a tremendous cheer burst
forth along both sides of the Straits.
The rest of the work was only
a matter of time. The most anxious moment had passed. In an hour and
thirty-five minutes after the commencement of the hoisting, the chain was
raised to its proper curvature, and fastened to the land portion of it which
had been previously placed over the top of the Anglesea pyramid. Mr. Telford
ascended to the point of fastening, and satisfied himself that a continuous
and safe connection had been formed from the Caernarvon fastening on the
rock to that on Anglesea. The announcement of the fact was followed by loud
and prolonged cheering from the workmen, echoed by the spectators, and
extending along the Straits on both sides, until it seemed to die away along
the shores in the distance. Three foolhardy workmen, excited by the day's
proceedings, had the temerity to scramble along the upper surface of the
chain--which was only nine inches wide and formed a curvature of 590
feet--from one side of the Strait to the other!*[2] Far different were the
feelings of the engineer who had planned this magnificent work. Its failure
had been predicted; and, like Brindley's Barton Viaduct, it had been freely
spoken of as a "castle in the air." Telford had, it is true, most carefully
tested every part by repeated experiment, and so conclusively proved the
sufficiency of the iron chains to bear the immense weight they would have to
support, that he was thoroughly convinced as to the soundness of his
principles of construction, and satisfied that, if rightly manufactured and
properly put together, the chains would hold, and that the piers would
sustain them. Still there was necessarily an element of uncertainty in the
undertaking. It was the largest structure of the kind that had ever been
attempted. There was the contingency of a flaw in the iron; some possible
scamping in the manufacture; some little point which, in the multiplicity of
details to be attended to, he might have overlooked, or which his
subordinates might have neglected. It was, indeed, impossible but that he
should feel intensely anxious as to the result of the day's operations. Mr.
Telford afterwards stated to a friend, only a few months before his death,
that for some time previous to the opening of the bridge, his anxiety was so
great that he could scarcely sleep; and that a continuance of that condition
must have very soon completely undermined his health. We are not, therefore,
surprised to learn that when his friends rushed to congratulate him on the
result of the first day's experiment, which decisively proved the strength
and solidity of the bridge, they should have found the engineer on his knees
engaged in prayer. A vast load had been taken off his mind; the perilous
enterprise of the day had been accomplished without loss of life; and his
spontaneous act was thankfulness and gratitude.
Menai Bridge
The suspension of the
remaining fifteen chains was accomplished without difficulty. The last was
raised and fixed on the 9th of July, 1825, when the entire line was
completed. On fixing the final bolt, a band of music descended from the top
of the suspension pier on the Anglesea side to a scaffolding erected over
the centre of the curved part of the chains, and played the National Anthem
amidst the cheering of many thousand persons assembled along the shores of
the Strait: while the workmen marched in procession along the bridge, on
which a temporary platform had been laid, and the St. David steam-packet of
Chester passed under the chains towards the Smithy Rocks and back again,
thus re-opening the navigation of the Strait.
In August the road platform
was commenced, and in September the trussed bearing bars were all suspended.
The road was constructed of timber in a substantial manner, the planking
being spiked together, with layers of patent felt between the planks, and
the carriage way being protected by oak guards placed seven feet and a half
apart. Side railings were added; the toll-houses and approach-roads were
completed by the end of the year; and the bridge was opened for public
traffic on Monday, the 30th of January, 1826, when the London and Holyhead
mailcoach passed over it for the first time, followed by the Commissioners
of the Holyhead roads, the engineer, several stage-coaches, and a multitude
of private persons too numerous to mention.
We may briefly add a few
facts as to the quantities of materials used, and the dimensions of this
remarkable structure. The total weight of iron was 2187 tons, in 33,265
pieces. The total length of the bridge is 1710 feet, or nearly a third of a
mile; the distance between the points of suspension of the main bridge being
579 feet. The total sum expended by Government in its erection, including
the embankment and about half a mile of new line of road on the Caernarvon
side, together with the toll-houses, was 120,000L.
Notwithstanding the wonders
of the Britannia Bridge subsequently erected by Robert Stephenson for the
passage across the same strait of the Chester and Holyhead Railway, the
Menai Bridge of Telford is by far the most picturesque object. "Seen as I
approached it," says Mr. Roscoe, "in the clear light of an autumnal sunset,
which threw an autumnal splendour on the wide range of hills beyond, and the
sweep of richly variegated groves and plantations which covered their
base--the bright sun, the rocky picturesque foreground, villas, spires, and
towers here and there enlivening the prospect-- the Menai Bridge appeared
more like the work of some great magician than the mere result of man's
skill and industry."
Conway Suspension Bridge
Shortly after the Menai
Bridge was begun, it was determined by the Commissioners of the Holyhead
road that a bridge of similar design should be built over the estuary of the
Conway, immediately opposite the old castle at that place, and which had
formerly been crossed by an open ferry boat. The first stone was laid on the
3rd of April, 1822, and the works having proceeded satisfactorily, the
bridge and embankment approaching it were completed by the summer of 1826.
But the operations being of the same kind as those connected with the larger
structure above described, though of a much less difficult character, it is
unnecessary to enter into any details as to the several stages of its
construction. In this bridge the width between the centres of the supporting
towers is 327 feet, and the height of the under side of the roadway above
high water of spring tides only 15 feet. The heaviest work was an embankment
as its eastern approach, 2015 feet in length and about 300 feet in width at
its highest part.
It will be seen, from the
view of the bridge given on the opposite page, that it is a highly
picturesque structure, and combines, with the estuary which it crosses, and
the ancient castle of Conway, in forming a landscape that is rarely equalled.
Footnotes for Chapter XII.
*[1] In an article in the
'Edinburgh Review,' No. exli., from the pen of Sir David Brewster, the
writer observes:--"Mr. Telford's principle of suspending and laying down
from above the centering of stone and iron bridges is, we think, a much more
fertile one than even he himself supposed. With modifications, by no means
considerable, and certainly practicable, it appears to us that the voussoirs
or archstones might themselves be laid down from above, and suspended by an
appropriate mechanism till the keystone was inserted. If we suppose the
centering in Mr. Telford's plan to be of iron, this centering itself becomes
an iron bridge, each rib of which is composed of ten pieces of fifty feet
each; and by increasing the number of suspending chains, these separate
pieces or voussoirs having been previously joined together, either
temporarily or permanently, by cement or by clamps, might be laid into their
place, and kept there by a single chain till the road was completed. The
voussoirs, when united, might be suspended from a general chain across the
archway, and a platform could be added to facilitate the operations." This
is as nearly as possible the plan afterwards revived by Mr. Brunel, and for
the originality of which, we believe, he has generally the credit, though it
clearly belongs to Telford.
*[2] A correspondent informs
us of a still more foolhardy exploit performed on the occasion. He says,
"Having been present, as a boy from Bangor grammar school, on the 26th of
April, when the first chain was carried across, an incident occurred which
made no small impression on my mind at the time. After the chain had reached
its position, a cobbler of the neighbourhood crawled to the centre of the
curve, and there finished a pair of shoes; when, having completed his task,
he returned in safety to the Caernarvon side! I need not say that we
schoolboys appreciated his feat of foolhardiness far more than Telford's
master work." |