The beginning of the 5th Century AD was the start of the end for roman Britain. In the year 407 Constantine III is proclaimed in Britain, after which he leaves the islands shores for Gaul, taking with him much of the already depleted garrison of Britain. Later in the year 410 Honorius, sends word that Britain is to look after its own defences, pressures from enemies all around the Empire were straining the defences closer to Rome. It would have been a gradual transition, i dare say that many of the Romano-British who were so used to Romes protection believed that the legions of Rome would once again defend their lush green lands. And life, for a time, would have gone on as normal. However, without the order that Rome brought the systems that held order would have started to collapse, many who had no power before would seek local power of their own, and Britain would slowly sink back into a more local and tribal governed place. Not to mention Scots, Saxons, Angles, Jutes and others who all were seeking riches and plunder from Romes withdrawal. It is around the middle of the 5th Century that the saxon invasion is said to have begun, theories differ from the Saxons surging into Britain in the wake of Romes withdrawal or that they were hired as mercenaries by rich Romano-British, seeking protection, and that seeing how ripe for conquest the land was they eventually turned on their "paymasters" and took what they wanted, inviting others from across the sea.
But what did all this mean for the former Roman fortress or Burgh castle. Being right on the eastern shore it was bang on the front line of invasion from the east. It may have been garrisoned for a time by the Saxon mercenaries (if this theory is correct) until they turned their attention inwards, as the flow of Saxon invasion began to intensify and spread inland the strategic position of the fort would become less important and relevant. The front line had been pushed inland and the eastern shore was now more a landing site for the invaders.
Accounts for the castle become very thin on the ground, but i did manage to find one reference to it. In the 630s Christianity was spilling out of Ireland into Britain, and a group of Irishmen led by a man called Fursa (later to become Saint Fursa) settled in east Anglia to spread the word of Christ, it is believed that Burgh castle could have been the sire where they built a monastery and burials were found there dating from the 7th to early 8th Centuries. Could this have been Fursas followers?
Much later following the Norman conquest in 1066 burgh castle was the site of a small earth and timber castle, built-in one of the corners of the fort, the earth work of which can still be seen today (upon my visit the grass was long so I was unable to see it).
So as you can see Burgh castle has a very rich and interesting history, and I dare say that many more clues lay beneath the ground, waiting to be discovered and add a new chapter to this once great fort of Rome. Today the site is owned by The Norfolk Archaeological trust and the walls of the fort are in the care of English heritage.
I strongly recommend a visit to this fort, take a minute to stand their and imagine the roman troops, many miles from home staring over the walls into the great estuary that was once there.