In the mid-late 13th century, the main entrance to Colchester Keep was strengthed by the addition of a masonry barbican, which incorporated an earlier fore-building.<1><2>

The earlier structure was stone built and has been tentatively dated to the early 12th century. Prior to this there is evidence for a rubble foundation which it is suggested could have supported only a light timber superstructure, possibly a staircase. The 13th century barbican abutted the keep and clasped the north-west corner of the chapel (MCC2084) , its plan takes into account (i.e. respects) the west door of the chapel. Its walls are built of fairly uniform small stones and morter, mostly septaria and include some Roman tile and glazed medieval roof tiles mostly in more or less continuous bonding courses. Some quoins are of greensand and septaria, others of tile. The main door lay in the west end of the south wall and was flanked by two solid D-shaped towers. East of the door are six, originally seven, loopholes, and in the east wall a loop and a doorway. Internally, the building is divided into two compartments by a wall 1.6m thick, pierced by a doorway at its north end.

A number of burials were found lying over the ruins of the Barbican, themselves sealed by demolition rubble of 1683.<1><2>

Between 1931 and 1934 a series of excavations were undertaken to the south of the Castle Keep by Dr. P.G. Laver, assisted by E.J. Rudsdale. Immediately to the south of the keep excavations in 1933-4 revealed two medieval forebuildings (incl. domestic hall), a barbican, a chapel, several inhumation burials and some earlier Roman features.<1>