Antiquarian and modern excavations at Castor, Cambs., have been taking place since the seventeenth century. The site, which lies under the modern village, has been variously described as a Roman villa, a guild centre and a palace, while Edmund Artis working in the 1820s termed it the 'Praetorium'. The Roman buildings covered an area of 3.77 ha (9.4 acres) and appear to have had two main phases, the latter of which formed a single unified structure some 130 by 90 m. This article attempts to draw together all of the previous work at the site and provide a comprehensive plan, a set of suggested dates, and options on how the remains could be interpreted.