Fort Denison was once a small, rocky island referred to by the local Aboriginal people as Mat-te-wan-ye, also spelt Muttewai.
After the First Fleet arrived in 1788, Governor Phillip renamed the land Rock Island, but it was informally known to locals as Pinchgut, as it was believed convicts were sentenced to weeks at a time isolation on the island with little bread and water.
The island was flattened and quarried for sandstone, which was used in the building of Bennelong Point, where the Opera House now stands. Once flattened, the fortification was completed in 1857. Built from 8000 tonnes of sandstone, quarried near Kurraba Point, Neutral Bay, the island was named Fort Denison after Sir William Thomas Denison who was the Governor of New South Wales at the time.
From 1906 to 1942, the 1 o’clock cannon was fired each day to enable sailors to correctly set their ship’s chronometer to the local time. The firing of the cannon was stopped during World War II to avoid terrifying Sydney-siders and was later resumed in 1986. Still to this day the cannon is fired at 1 o’clock by the National Parks Guide.
The island has been managed by various organisations over time, including the Naval Brigade in 1869, and the Sydney Harbour Trust in 1900. Fort Denison became part of Sydney Harbour National Park in 1992, managed by the New South Wales National Parks & Wildlife Service.