square keep, a mound, strong circumscribing earthworks, and beyond the church an advanced bank and ditch of formidable dimensions. It is evident that those who laid out these earthworks were well aware of the peril of the position. Bishop’s Castle or Lydbury is well within the frontier. It was the residence of the bishops of Hereford from 1085 to 1154, and was taken by storm in 1235. By their possession of this castle the bishops became Lords Marchers. Montgomery was the centre and one of the most exposed castles of the frontier. It occupied the summit of a steep rock, and was almost impregnable. It has, however, been taken, destroyed, and re-built at least twice, so that little, if any, of its masonry is of the time of Earl Roger. It stands just within the dyke. North of Montgomery, and protected by the well-known Long Mountain, is Cause Castle or Alreton, the earliest seat of the Corbets, who named it from the Pays de Caux, whence they came. It was built towards the close of the reign of the Conqueror, and is remarkable for its massive keep and capacious well, and for the rare example of the substitution of a Norman for a native name. North of Cause is Abberbury, the seat of the Fitz Warines before they held Whittington. It was held under Cause. Knockin Castle, the head of the Barony of Strange, was probably built by Guido le Strange in the reign of Henry II. Far more exposed, and having the mountainous ground of Denbigh in its front, is Oswestry, supposed by Mr. Eyton to be the Castel Luare (L’Ouvre) of “Domesday,” the work of Rainald de Ballieul, and long celebrated as a seat of the Earls of Arundel. It is now reduced to a mound and the foundations of a keep. The outworks have been levelled and built over by the encroaching town, and the ditches filled up. The town walls are also removed. Very near to Oswestry is Whittington, founded as a Norman work by William Peverel in 1138, but better known from its later lords the Fitz Warines. This is the castle that defied the Welsh in 1223, and the strength of which lay not only in its shell keep, towers, and gatehouse, parts of all which remain, but in a curious arrangement of outworks in earth, with several broad and deep ditches connected with a morass, the limits of which may still be traced. The original mound, scarped and enclosed like Bungay in a revetment wall by the Norman engineer, is a good example of the manner in which those early fortifications were adapted to the masonry of later times. Ellesmere is a Peveril castle, but was held by the Welsh Princes as late as the reign of Henry III. Whitchurch was founded probably by William de Warren, whose wife was stepdaughter to the Conqueror. It was the Weston of “Domesday,” and by a singular inversion became widely known afterwards as Blackmere. These complete the outer line of defence of the Middle March.