A well-preserved twelfth century earthwork motte and bailey fortress. The construction rises abruptly from the west bank of the Clyde. The motte has been raised on a river terrace and has an unusual, sub-triangular shape on plan that narrows to a point on the south side. It measures 28 metres from north to south by 20 metres transversely at its widest point, and stands to two metres in height above the bailey. The top of the motte is 22 metres by 11 metres in extent. It is surrounded by a ditch 10 metres in breadth by up to 2 metres in depth. The rampart appears to be constructed of gravelly clat obtained from the ditch. There is a slight dip in the west-north-west of the motte, which may mark the site of an entrance. However, a slight bank along its edges and other minor features on top of the motte may be a relic of the construction of the twentieth century monument to Matthew McKendrick, a local postmaster and keen fisherman who died in 1926, or excavations that took place in the nineteenth century.