Colchester is a city in Essex, England. It is the third-largest settlement in the county, with a population of 130,245 at the 2021 Census. The demonym is Colcestrian. Colchester occupies the site of Camulodunum, the first major city in Roman Britain and its first capital. Colchester therefore claims to be Britain's first city. It has been an important military base since the Roman era, with Colchester Garrison currently housing the 16th Air Assault Brigade.