It was doubtless due to the exigencies occasioned by those frequently recurring wars and raids from the 13th to the 16th century that the whole country on both sides of the frontier became so thickly studded with castles and peel-towers, the numerous ruins of which still form a distinctive feature in Border scenery, although from times much earlier the castles and strongholds were characteristic elements in the old Scottish landscape. Alexander Hume, of Polwarth, the poet-preacher of Logie, near Stirling, in his fine description of a "Summer's Day," thus refers to them:-- "The rayons of the sunne we see Diminish in their strength; The shade of everie tower and tree, Extended is in length. Great is the calm for everie quhair The wind is settlin' downe; The reik thrawes right up in the air, From everie tower and towne." Generally these towers were planted on heights overlooking the river-valleys, and, as a rule, within sight of one another, in order that the signals of invasion or alarm--flashed by means of the bale fire--might be the more rapidly spread from point to point. Very few of them are now entire--the best-preserved on the Scottish side being, perhaps, Barns, at the entrance to the Manor valley; Bemersyde, still inhabited; and Oakwood on the Ettrick, incorporated in the present farm buildings; and on the English side, Corbridge and Doddington and Whittingham. From a return made in 1460 we find that Northumberland alone possessed 37 castles and 78 towers, and the Scottish side was equally well strengthened and defended. Amongst the larger and more important fortresses on the English side were the Castles of Alnwick, Bothal, Carlisle, Cockermouth, Coupland, Dilston, Elsdon, Etal, Ford, Naworth, Norham, Prudhoe, Wark, Warkworth; and on the Scottish side, Berwick, Branxholme, Caerlaverock (the true Ellangowan of "Guy Mannering"), Cessford, Ferniherst, Hermitage, Hume, Jedburgh, Neidpath, Peebles, Roxburgh, Threave, Traquair, besides, as has been said, hundreds of peel and bastle-houses scattered all over the country.