character is apparent, except perhaps scattered rocks at low tide. However, on close inspection the sandstone bedrock visible below the south west battery reveals part of the rock of the island, particularly when combined with the pictorial evidence provided by drawings such as that by Barrington in 1802. The Fort The visual impact of the fort is a combination of the strong vertical mass of the Martello tower and the equally strong horizontal lines of the low barrack and battery buildings. The two distinct building forms reflects the history of the staged Fort construction; which progressed from the original horizontal form of the battery, and later construction of the barracks and Martello tower. The tower, which only lost its dominant role in marking the water entrance to the city with the construction of the Sydney Opera House, was built with an open gun platform (terreplein) which surmounted two internal levels. A section through the tower, shows the navigational light which replaced the upper cannon in 1913. The lower internal level contained rooms for the storage of gunpowder and provisions and the middle level still houses the three original cannons. Internal tower circulation is via a spiralling staircase that connects the three tower levels. External access to the tower is through a single external door from the upper terrace level battery and bastion.Three major elements comprise the strong horizontal section of the fort; the battery and bastion, the barracks and terrace. Gun Battery and Bastion The outward facing defensive side of the fort known as the gun battery and bastion confronted incoming ships. It is constructed out of the island's sandstone bedrock. The battery consists of an open working area which services a series of nine gun placements and corresponding slanted firing openings which are equally positioned along the raised parapet wall of the battery. An underground water tank has been cut into the bedrock of the battery. The bastion located at the southern end of the battery was constructed to house a single cannon set behind a raised stone parapet. The cannon was located on a raised circular revolving mount to maximise the cannon's aim of fire. Wet Ditch and Breakwater A wet ditch and breakwater formed by sandstone blocks separates the fort from the open harbour channel. Beyond this is a breakwater which surrounds the whole island which moderates the wave action against the stone fabric of the fort.