OS grid reference :-
The village of Old Grimbsy is situated on the island of Tresco.
Old Grimsby has a quay, at the southern end of which stands the Blockhouse, a sixteenth century fort built to defend the harbour from attack. King Henry VIII built a series of fortifications along the English coast to defend it against his French and Spanish foes, but the Isles of Scilly were left undefended. During the reign of his son Edward VI, the Old Blockhouse and King Charles' Castle were constructed between 1548 and 1550.
The Old Blockhouse was probably the earliest of the defences on Tresco. It consists of a square, paved platform which would have accommodated three guns. On the south side there are the remains of a locker, probably used for gunpowder, and attached to the west side there is a small room with two windows and a fireplace which would have offered shelter for the garrison. Around the building there is a shallow bank that could date from the mid sixteenth century or from the period of the Civil War when the Old Blockhouse was at the heart of the fighting on Scilly.
Cromwell's Castle, (pictured right) named after the Parliamentary leader, was constructed by Sir Robert Blake following the Parliamentary invasion of the Isles of Scilly in 1651. During the Civil War between 1642 and 1646, the Scilly Isles had been firm supporters of the Royalist cause of King Charles I, and rose in rebellion against Parliament in 1648. Tresco became a base for Royalist privateers and Parliament became concerned that the Dutch, then hostile to England, might exploit the situation. Accordingly, in 1651 they despatched Robert Blake and a naval force to retake the island