Trematon Castle is situated near Saltash in Cornwall, United Kingdom. It is similar in style to the later Restormel Castle, with a 12th-century keep. Trematon Castle overlooks Plymouth Sound and was built probably by Robert, Count of Mortain on the ruins of an earlier Roman fort: it is a motte-and-bailey castle and dates from soon after the Norman conquest. It occupies a sentinel position one and a half miles south-east of Trematon village ().