A Claudian Fort with an annex that was built over by the later Roman Town. Dendrochronoligical evidence finds that it was built in the winter of 43-44. The main fort was overbuilt, but the western annex is reasonably intact archeologically. A retired veteran's tombstone indcates that the fort was garrisoned by the 2nd Augustan Legion, commanded at the time by Vespasian. It is probable that the fort was built under the future emperor's orders.
See: http://roman-britain.co.uk/places/alchester.htm
http://www.associationromanarchaeology.org/ARA_Bulletin13.pdf
http://www.blhs.org.uk/uploads/Military/Alchester%20-%20Current%20Archaeology,%202005.pdf