 A 1791 book states it has a ""summit"..." [of] ""half a Scots acre"" (approx.0.25 hectare) and ""rises 38 feet"..." (11.6 metres) ""above a small plain on the"..." north-east ""but is only 12 or 14 feet"..." (3.7 or 4.3 metres) ""above the higher ground"" to the south-west.The first construction on Castlehill was a small late middle age, 12th century ""timber castle or Motte"" built to protect the estuary.