![](http://darkwing.uoregon.edu/~mharrsch/Portchester.jpg)
Topographic and geophysical surveys of the ancient site have revealed a number of previously uncharted structures dating from Roman, Saxon and medieval times. "
In the outer bailey features were discovered that relate to the Roman, Saxon and medieval periods of the site. Between the inner and outer ditches possible remnants of the Roman fort and a number of medieval and post-medieval structural features were detected.
Portchester’s outer defences incorporate the well-preserved remains of a Roman fort. It is thought to have been established between AD 285 and 290 by Marcus Aurelius Carausius who was instructed by the Emperor Diocletian to clear the seas of pirates.