The early castles of Peebles and Selkirk, as in other parts of Great Britain, were at first palisaded earth-works upon which were erected strongholds of timber. Hence Peel, which at first meant a wooden stockade, from the French pel Latin palus, a stake, came to designate a fortification with a building inside it, the enclosure as distinct from the building being known as the barmkyn. This wooden building was strengthened with an exterior coating of turf and clay. To prevent this wall of turf and clay from collapsing, the rigid structure of timber was built with its four sides sloping inwards, and when stone and lime were substituted for wood and turf the pyramidal form was preserved. In 1535 every landed Borderer possessing £100 worth of land was compelled by law to build a barmkyn of stone and lime upon his heritage and lands, with a tower in the same if he thought fit. It was at this time, therefore, that most of the Border keeps of stone and lime were built.

Of the first period (1200—1300) of military architecture in Scotland, no examples exist in Peebles or Selkirk. A distinct break takes place between the thirteenth- and the fourteenth-century type of castle. The country had been impoverished by the Wars of Independence. Besides, Bruce’s policy was to build small and inexpensive strongholds, easy to replace and of little value to the English invader. The second period (1300-1400) is therefore, characterized by small keeps, simple towers; later by keeps of L-shaped plan; and still later, or in the case of wealthy owners, by keeps of E (courtyard) plan. Tinnis Castle, near Drummelzier, so like a robber’s castle on the Rhine, built in this century, is exceptional in having four round towers, one at each corner, united by curtain walls. Little remains of it except the foundations.

Neidpath Castle was originally a peel tower, dating probably from the twelfth century. It belonged to the Fraser family and in the fourteenth century came into the hands of the Hays, afterwards earls of Tweeddale. In 1650 it was fortified by John Lord Yester, and besieged by Lambert. The castle, which is of L-shaped plan, is picturesquely situated in a wooded gorge on a rocky prominence overlooking the Tweed winding its way into the valley as it opens out towards Peebles. The walls, which form two oblique angles, are 10 to 11 feet thick. The original door was on the south or precipitous side above the river, and the upper floors were reached by a spiral stair. The tower is divided into two principal compartments by a vault. There is also a vault near the level of the parapet, and probably another carried the roof. Each principal compartment was divided once more into two by wooden floors. The great hall was on the second floor, immediately above the central vault, and was 40 feet long by 21½ feet broad. The corners of the building are all rounded, and the parapet, also rounded, has no projecting bartizans. In the seventeenth century the castle was greatly altered by the second earl of Tweeddale. A courtyard was made to the front, east side, the entrance changed to the centre of this front, a wide staircase introduced, the top storey heightened, the battlements raised so as to. contain small apartments, and the parapet fronting the courtyard left open, which was probably the balcony whence the "Maid of Neidpath" viewed the return of her lover, whose failure to recognise her broke her heart.

The third period (1400—1542) still had its simple keeps, of which Newark Castle is a fine example; keeps with one or two wings; and keeps enlarged into castles surrounding a courtyard.

"Newark’s stately tower
Looks out from Yarrow’s birchen bower,"

four and a half miles from Selkirk. In contrast to an older castle, Newark, completed for James III in 1470, means "New Work," and is in a better state of preservation than the other strongholds in Yarrow. It was a royal hunting seat in the times of the Stewarts. After the battle of Philiphaugh, 100 prisoners were shot in its courtyard; and it was occupied by Cromwell in 1650. The Duchess of Buccleuch, wife of Monmouth, resided here after his death, and it is during her time and in this castle that Scott makes the "Last Minstrel" sing his Lay. The castle is an oblong keep, 65 feet by 40 feet, with walls 10 feet thick and about 84 feet in height. It is surrounded by a barmkyn of irregular shape, about 150 feet square. The first floor is noticeable as it has the hall at one end, and the kitchen at the other with a great fireplace having a seat-cupboard and two mural closets.

To the fourth period (1542—1700) most of the strongholds in Peebles and Selkirk belong. These were mostly abandoned in the seventeenth century or developed into mansion houses. The castles which belong to the period are Thirlestane, Gamescleuch, Dryhope, Blackhouse, Kirkhope, Oakwood, Barns, Castlehill, Posso, Horsburgh, Nether Horsburgh, Hutcheonfield—all simple keeps; Buckholm, Drummelzier, Cardrona, Haystoun House, have an additional wing added to one end of the main block.

Drochil Castle is an example of the Z plan, having a tower at two of the diagonally opposite angles of the rectangular block so that its defenders might sweep with fire all its four sides at once. The castle has a magnificent situation near the junction of the Tarth and the Lyne. It commands views northwards up the Lyne, westwards up the Tarth, south and east down Lyne valley towards the Tweed valley and the hills behind Hundleshope. The castle is a transition building, and marks the change from the military peel tower with single tenement rooms to a double tenement building in which the military are less pronounced than the domestic features. The towers, for example, are small compared with the size of the building and the shot-holes have been made for musketry, not for cannon. A corridor 12½ feet wide on each storey divides the building into two blocks. The south block now consists of only one storey, but from the northern block it can be seen that the castle had four storeys with attics, each storey being reached by a circular staircase, which began on the ground floor at the front entrance. There were two entrances one at each end of the gallery on the ground floor, the west being the main one. Above this entrance are still to be seen in the tympanum the initials J. D. (James Douglas), the heart and the fetterlock, a D-shaped hobble for a horse, the badge of the Warden of the Marches. The ground floor contains the vaults and cellars, and in the N.E. angle a large kitchen with an immense fireplace and chimney still intact of equal width from floor to roof. The roof of the ground floor is vaulted, and the large hall above this vaulted roof in the south block was the dining room. Although the castle was unfinished when Morton was executed, it seems to have been occupied as a stronghold.

Hallyards is an example of the T plan; Elibank, Whytbank, Torwoodlee of the E or courtyard plan (Scottish type); Traquair of the courtyard plan (Renaissance type), while Fairnilee shows development of a keep into a house and mansion.

The situation of the keeps was chosen mainly for the purpose of giving and receiving fire signals. One fire meant that the enemy was approaching, two that he was coming indeed, and four "all burning together like candles" that he was in great force. The signals passed zigzag from one side of the river to the other up the main valley and its lateral streams till, having been seen all up Teviotdale, Ettrick, Yarrow, and Tweeddale, there gathered by early morning as many as 10,000 men at the rendezvous.

The ground area of the peel-towers often did not exceed 20 feet square. Barns is 28 by 20 feet. The hall on the first floor is only 174 by 14 feet. It is, therefore, not easy to explain how the owner of a small keep found accommodation for his family and retainers. Originally the first floor of the peel would be reached by a ladder, drawn up when the tower was closed. The ground chambers had always stone vaulted roofs. The bastel houses of Peebles, relics of which were to be seen a few years ago, had both stone vaulted roofs and outside stairs corresponding to the ladder of the peel. The entrance to the vaulted chamber of the peel was by a stout wooden door studded with bolts, and often protected by an iron "yett," the horizontal and vertical bars of which were interlaced to give it additional strength. The "yett" at Barns, probably the oldest in Scotland, is an example of this style of grating. In time the outside approach was dispensed with for, a narrow spiral staircase from top to bottom of the tower, generally situated in one of its angles and sometimes in the thickness of the walls. The narrow slots in the walls, deeply splayed on the inside, were meant for arrows; the round holes for fire-arms. The outside of the round holes at Drochil are filleted so as to reduce the chance of shots getting inside, but deeply splayed on the inside so as to increase the angle of fire for the defenders. The bartizan was the narrow passage between the roof and the battlements. Here the warders kept watch, and here the defence was carried on. Newark and Kirkhope have a bartizan on all sides; Neidpath on west and east. Barns and Oakwood have none. The furnishings depended on the wealth and rank of their owners and on the period. Jamie Telfer had:

"...naething in his house,
But ae auld sword
‘That hardly now wud fell a mouse";