There are Roman towns in East Anglia whose sites are known, and in many cases their names are known as well. With Caister-on-Sea and Burgh Castle there is some discussion about which of these forts was called Gariannonum, but it was certainly one of the two; where Sitomagus is concerned however, we have the name of the place without having a clue where it was located.
This Roman town was perhaps, after Venta Icenorum (Caistor St Edmunds), the major settlement in what was later to be termed East Anglia. Unlike Caistor, however, where the walls are still standing tall for anyone to see, nobody knows exactly where Sitomagus was. From the Antonine Itinerary we know that it was south of Caistor and north of Coddenham (Combretovium), and slightly nearer to the latter. The Antonine Itinerary was a third century document giving details of main road network in the Roman Empire. The distances are given, but the careless copying of the document over the centuries makes them of dubious validity; the original Antonine Itinerary has been destroyed long ago. Another document giving the site of Sitomagus is equally unreliable, and of course the two do not agree.
A number of sites have been suggested for the location of Sitomagus. In the book Memorials of Old Norfolk, published over a hundred years ago, Dunwich was advanced as a possible location, only to be rejected in favour of Thetford. Thetford was originally proposed as Sitomagus by William Camden (1551-1623), the antiquarian. Recent researches have dismissed Thetford as the location, but still put Dunwich forward as a possibility. Since the major part of the town of Dunwich now lies a mile out to sea, archaeological investigation is impossible. Even if it were plausible to explore underwater, the waves would have reduced any artefacts to an almost meaningless jumble. However, like the writer of Memorials of Old Norfolk in 1908, modern historians think Dunwich an unlikely choice. Their reasons centre on the meaning of the last syllables of the name, ‘magus’, which denotes a market. A coastal position is an unlikely place for a market, which ideally draws in produce from all points of the compass; with sea occupying so much of the surrounding geography the number of customers would be reduced. The same objection would seem to rule out the coastal town of Southwold. At least with Thetford no longer a candidate, we can be fairly sure it was in Suffolk.
Of the other towns in this part of Suffolk, Saxmundham would just about fit the vague directions we have, but Stowmarket would seem to be too far west. Both these places have at one time or another been suggested as sites for Sitomagus. Although it is shared by no-one else, my own favourite location for Sitomagus was Stradbroke; this town would fit the distances as they have come down to us, but it does not seem to have had a Roman past.
Among Suffolk archaeologists the favourite location for Sitomagus is currently the tiny spot in Suffolk known as East Green. Today this is much less than a villager or even hamlet, being little more than a farmhouse and a level crossing on the East Suffolk railway. It is true there is Roman archaeology in the area, but other places in Suffolk may also lay claim to such remains. There is at present nothing there to suggest a large town.
Although about half a dozen villas have been identified in Suffolk, and there is evidence of extensive occupation round Mildenhall (including a villa), nothing of Roman date remains visible above the ground anywhere in Suffolk as far as I am aware. There is certainly nothing to compare with Burgh Castle or Caistor St Edmund, nor even with what remains at Caister-on-Sea, where the ruins of the fort have been exposed in an archaeological dig in the 1950s. Nothing now remains visible at Brancaster, but this Fort of the Saxon Shore was only demolished in the 18th century by the local landowner.
So Sitomagus is a vanished town. If a large Roman town were to be discovered in East Suffolk, the likelihood of this having been the place would be strong, but we could never be really sure. There would always be nagging doubt that an even larger town remained to be discovered.