Mersea Fort, also known as Cudmore Grove Blockhouse, was an artillery fort established by Henry VIII on the East Mersea coast in 1543. It formed part of the King's Device programme to protect against invasion from France and the Holy Roman Empire, and defended the River Colne that led to the town of Colchester. It was triangular in shape, with earthwork walls and three bastions to hold artillery. It was demobilised in 1552, but was brought back into use several times over the next century and saw service during the Second English Civil War of 1648. The fort hosted an admiralty court to oversea the local oyster trade, until the dilapidation of the site forced the court to move to the Moot Hall in Colchester in the middle of the 18th century. A new gun battery was built at the fort during the Napoleonic Wars, but the fortification then fell into decline and was extensively damaged by the construction of a sea wall along the coast. The remains of the earthworks were excavated by archaeologists between 2002 and 2003. History 16th – 17th centuries Mersea Fort was built as a consequence of international tensions between England, France and the Holy Roman Empire in the final years of the reign of King Henry VIII. Traditionally the Crown had left coastal defences to local lords and communities, only taking a modest role in building and maintaining fortifications, and while France and the Empire remained in conflict, maritime raids were common but an actual invasion of England seemed unlikely. Modest defences based around simple blockhouses and towers existed in the south-west and along the Sussex coast, with a few more impressive works in the north of England, but in general the fortifications were limited in scale. In 1533, Henry broke with Pope Paul III over the annulment of his long-standing marriage to Catherine of Aragon. Catherine was the aunt of Charles V, the Holy Roman Emperor, who took the annulment as a personal insult. This resulted in France and the Empire declaring an alliance against Henry in 1538, and the Pope encouraging the two countries to attack England. An invasion of England appeared certain. In response, Henry issued an order, called a "device", in 1539, giving instructions for the "defence of the realm in time of invasion" and the construction of forts along the English coastline. The county of Essex was not a