A fort has stood at this site since at least 1822. However between 1830 and 1839 significant improvement works were undertaken to, amongst other things, the fortifications and gun emplacements.
Originally named Fort Cockburn, it became more commonly known as Fort Thornton, a name recorded since 1830.
The fort is mounted on a rock promontory and faces northwest. It has been significantly modified over time and its current configuration is due to rebuilding work undertaken post 1880, along with other modifications undertaken during World War One and World War Two. The most obvious remnant of the original fortifications is the ground floor and underground cistern of the two storey stone blockhouse, which was completed in 1839.
Other fortifications were built to compliment and support Fort Cockburn; Fort Hayes to the west, Fort Warren to the immediate east, a battery on the slopes of Cross Hill, possibly below Bate’s Cottage, another immediately west of the cottage and eventually Fort Bedford above and also to the west.
Access to the fort is via an east sloping ramp on its south east side. The remains of a cast iron water pipe which supplied the block house cistern is still in place and may date from the completion of the cistern in 1835.
This fort itself was renamed Fort Cockburn in the 1970s in honour of Bobbie Cockburn, chair of the London Users Committee. He was a relation of Admiral of the Fleet Sir George Cockburn who was responsible for the transport of Napoleon I to his exile on St Helena following his defeat at the Battle of Waterloo, and whom after the fort was originally named.
This fort is open to the public throughout the day.