Fortification began with construction of gun batteries in the mid-16th century on the two islets in St Aubin’s Bay. The western one outside the older St Aubin’s Harbour later became St Aubin’s Fort, and the eastern one off St Helier, which albeit was the Island’s town and capital, didn’t yet have a usable harbour. The first major fortification works began a few decades later and the New Castle, as originally known, was christened Elizabeth Castle by Sir Walter Raleigh, the Island’s Governor between 1600 and 1603 in honour of Queen Elizabeth I.
Improved and extended over the following centuries, Elizabeth Castle was the Island’s main fortress until the construction of Fort Regent in the early 19th century. The Castle was fortified by the Germans in the Occupation as part of the defences around the harbour and its approaches.