Trematon Castle stands on an eminence rising steeply above the River Lynher, two miles southwest of Saltash and the Tamar estuary. Robert, Count of Mortain and Earl of Cornwall probably founded the castle. It is referred to as his in the Domesday Book. At that time Trematon was a place of some importance whereas now it is scarcely a village. The castle saw action in the Civil War and, earlier, in the course of Kilter’s Insurrection which broke out in Cornwall in 1594. The rebels laid siege to the castle and managed to lure out and capture its defender, Sir Richard Grenville.
Trematon is a fine example of a motte and bailey castle. It is even more notable for the excellent preservation of its late Norman masonry, almost certainly the work of Henry de Dunstanville. An oval shell keep crowns the motte and a plain curtain surrounds the bailey. Both keep and curtain retain their crennelations, the latter having unusually narrow merlons. Until 1897 the curtain stood complete, but in that year a long portion was removed to supply materials for the house that stands in the bailey. Consequently, there is now a long gap between the gatehouse and the southwest corner of the bailey.
At the foot of the motte is an original postern. He main entrance is through a perfectly preserved gatehouse added by Reginald de Valletort around 1250. Its square plan is decidedly old-fashioned at a time when round-towered gatehouses predominated. Nevertheless, the gatehouse projects entirely outside the line of the curtain, so that it acts as a powerful flanking tower, and the gate passage was defended by two portcullises and a pair of gates between them. The ascent through the gate passage is an obstacle in itself. Note the first arrow slits of the castle, both the cross-slits on the keep parapet and the slits with roundels in the gatehouse.