was a citadel style fort constructed as part of the first defensive works of the penal settlement of Sydney
ordered a fort to be built on the site of Windmill Hill to defend the colony from rebellious convicts and possible French
attack in 1803
. The fort was never fully completed and never fired a single shot in anger.
A flagstaff was built in 1825 on the eastern wall of the fort, which sent messages to ships in the harbour and the signal station at Fort Denison and South Head.
In 1840 a new signal station, designed by the colonial architect Mortimer Lewis, was built to replace the flagstaff. The fort was subsequently demolished leaving the eastern rampart as the only remaining evidence of the fort's existence.
Sydney Observatory was built on the site in 1858 to provide accurate time readings for the colony and to observe stars in the southern sky.