The Roman fort of Londinium (City of London, England) was built around AD120, just north-west of the main population settlement.
It covered 12 acres and was almost square in size, 200m along each length. As Londinium grew, the fort was later absorbed into the defensive wall that surrounded the city.
The fort could house up to 1000 men and provided suitable barracks and gated entry.
However, a century later the site was decommissioned and buildings dismantled as the military situation in the southern edge of Britannia had become more secure.
Today, the forts northern and western edges still remain visible, along with Saxon fortifications and medieval bastion towers as part of the Barbican and Museum of London complex.