Fort Williamsburgh was built by Sir Thomas Wynn in 1761, later additions are of 1773-6. Thomas was MP for Caernarvonshire, Constable of Caernarvon Castle and Lord Lieutenant of the County, and took his responsibility for the County Militia seriously.
The fort is roughly square with angle bastions linked by ramparts and surrounded by a ditch. The gatehouse resembles a garden pavilion. There are a variety of domestic and military buildings within.
The fort was the focal point for the 'Society or Garrison' and the associated 'Holy Order of Sisterhood'.
It remains a prominent feature of the park (NPRN 86377) of Glynllifon mansion (NPRN 26526).

Source: RCAHMW Caernarvonshire Inventory II (1960), 187-8

John Wiles 09.05.07