04 March, 2010

Birdoswald Roman Fort: dating the post-Roman use of the site

In an earlier post, I described the post-Roman timber halls constructed on the site of the north granary in the Roman fort of Birdoswald on Hadrian’s Wall. We know the halls are post-Roman because late Roman coins of Valentinian, dated to the 380s, were found beneath the relaid floor. How long did the site remain in use after the end of Roman occupation?

Dating the post-Roman halls

Unfortunately, there are no surviving timbers from the post-Roman timber buildings that could be dated by dendrochronology or radiocarbon, and there are no datable objects from the site after the coin of Theodosius found under the collapsed roof of the south granary (Wilmott 2001 p. 123). So dating the post-Roman halls is a matter of interpretation.

There are two distinct timber building phases to accommodate, the first one built more or less directly on top of the north granary and the second one built partly on the north granary and partly on the adjacent street. Both must post-date the coins of Valentinian found under the flagstone floor, so both must post-date the 380s. If the timber buildings replaced the function of the south granary, whose roof collapsed some time after the worn coin of Theodosius (388-395) was dropped on its floor, they also post-date this collapse.

Tony Wilmott suggests that the south granary roof collapsed in the early fifth century, say around 420, as the coin of Theodosius was very worn and thus had been around for some considerable time. If the first timber building on the north granary site was constructed around this time, and if each phase had a life of 50 years, this would suggest the second timber building was constructed around 470 and lasted until around 520 (Wilmott 2001 p. 123-4).

Needless to say, these are very approximate estimates. Timber buildings can and do last a lot longer than 50 years if the structural timbers are supported on stone foundations (as both the Birdoswald buildings were), as witness the medieval and early modern timber-framed buildings that still survive in Britain today. Conversely, a timber building can have a life considerably shorter than 50 years if bad weather, accidental damage, poor construction or bad luck intervene, or if the owner simply decides he feels like replacing it. And although a collapsed building is unlikely still to be occupied, the reverse is not necessarily true; a building could be abandoned for social, political or personal reasons long before it actually falls down. The issue date of a coin can be identified accurately, and this gives the earliest possible date for its loss or deposition, but the actual date of its loss or deposition could be later, perhaps much later, than its date of issue, depending on how long the coin was in circulation (or in storage).

Furthermore, it’s difficult to be sure whether a site was continuously occupied or whether it went in and out of use, if the periods of disuse were too short for archaeologically recognisable deposits to form, or if any such deposits were cleared at subsequent re-use rather than built over. Ken Dark reviews the same sequence of evidence from Birdoswald and proposes a break in occupation between the residential use of the south granary and the buildings constructed on the north granary. In this scenario, he suggests that the south granary was in use as a residential hall during the last decades of the Roman occupation (roughly 350 to 400), that the fort was then abandoned for a period after the end of Roman government, and that the fort was re-occupied some time during the later fifth or sixth century, at which time the site of the north granary was cleared and the timber buildings constructed (Dark 2002, p.198-199).

Another possibility that occurs to me is that there may have been a break between the first and second timber building phases. Since the second timber building was partly on top of the site of the first, the first must have collapsed or been demolished before the second one could be built. Demolition and building might have been quite quick, if all the required materials were assembled and pre-prepared on site beforehand, but that requires efficient logistics and even then the replacement of one building by the other could hardly have been the work of a day. Abandonment of the site, perhaps only briefly, allows for site clearance and the subsequent construction of the second timber building.

It is worth bearing in mind that abandoning the area of the granaries does not necessarily mean abandoning the entire fort site. Areas of occupation may have moved around according to the condition of existing structures and the availability of sites for rebuilding. A barrack-type building constructed in the late Roman period (later fourth century) had re-used an inscription from the commanding officer’s house (praetorium) and another inscription commemorating the rebuilding of the granary, indicating that these buildings had gone out of use while other areas of the site were still occupied and in use.

Only the area around the west gate at Birdoswald has been excavated to modern standards, and it is possible that other early medieval structures may have stood elsewhere in the fort. Early excavations would not have picked up the slight traces left by timber buildings, and parts of the fort interior have not been excavated at all. Medieval ridge-and-furrow plough marks cover the southern third of the fort interior, with the exception of an area in the south-west corner where there is also a long flat platform against the fort wall. This has been suggested as the site of a medieval building (Wilmott 2001, p.133, 135); if so, perhaps the area might also have been in use earlier. The foundations of a square tower, possibly dated to the fourteenth/fifteenth century, were discovered in excavations north of the west gate (Wilmott 2001 p. 137). The west gate was probably still standing when the tower was built, as the pottery found under the rubble of its collapsed arch indicates it collapsed in the later fifteenth century, and Wilmott suggests that the first-floor storey of the gate was re-roofed and used as a hall building to go with the tower (Wilmott 2001, p. 138). If the west gate was sufficiently intact to be re-roofed and occupied as a hall in the fourteenth century, perhaps the same also applied several centuries earlier.


It’s clear from the timber halls that occupation at Birdoswald continued beyond the end of Roman government in Britain, for an unknown period that was long enough to construct two successive large timber buildings on the same site. The size of the halls implies that whoever ordered their construction controlled substantial resources of materials and manpower. It’s a reasonable inference that this was a local or regional ruler.

Although the halls are built on a Roman site, and the first one directly re-used surviving Roman walls as part of its structure, they are built of timber not masonry. This implies that Roman building techniques had been lost, either due to lack of knowledge or lack of the infrastructure to obtain the appropriate materials, or deliberately rejected.

The duration of post-Roman occupation is unknown, but must surely extend until at least well into the fifth century, unless the timber buildings had absurdly short lives, and could easily extend well into the sixth century or beyond, particularly if there was a break in occupation. The long cist grave found nearby is consistent with a burial of early medieval date, and is consistent with its occupant having been a Christian. One could speculate that the long cist grave represents the burial of a Christian ruler who lived in the timber hall, but this really is clutching at straws.

The eighth-century pin found nearby may indicate that the site was in use at this date, especially if the timber halls on the north granary site were succeeded (with or without a break in occupation) by other structures elsewhere in the fort, but this is unsubstantiated.

The place name, combining an Old English personal name with a Brittonic topographical description (“pen or farmyard of Oswald”) is most likely to have been coined some time in the early medieval period in the centuries after the end of Roman rule (since no trace of the Roman name remains in the modern name), but before the eleventh century when Old English names largely went out of fashion following the Norman Conquest and perhaps more likely before the Norse/Viking influence of the ninth and tenth centuries. The absence of any trace of the Roman name of the fort, Banna, in the modern name is consistent with a period of abandonment at some time after the end of Roman rule, long enough for the name to be lost, followed by re-occupation some time in the early medieval period. However, it could also be consistent with deliberate replacement of the old name by someone who wanted to emphasise a change of ownership or political allegiance. Whether “Oswald” refers to the sort of individual who might have owned and feasted in the timber halls, or to a humbler farmer working the site as agricultural land, or anything in between, is anyone’s guess.

On the whole, I would say that occupation until well into the sixth century is supported by the timber halls. This could represent continuous occupation without a break from the Late Roman period, or could represent reoccupation of a temporarily abandoned site. Further occupation into later centuries – with or without a break - is not unreasonable, but the only evidence for it is the eighth-century pin and perhaps the place name, which is not exactly definitive.

If Birdoswald was the base of an important local ruler in the later sixth century, this brings it into the same sort of period as the battle of Arthuret, entered in the Annales Cambriae in 573. Arthuret is traditionally located near Longtown in Cumbria, which is less than 20 miles from Birdoswald. I mentioned Arthuret in my article about Peredur. More about the battle in a later post.

Dark K. Britain and the end of the Roman empire. Tempus, 2002. ISBN 0-7524-2532-3.
Wilmott T. Birdoswald Roman fort: 1800 years on Hadrian’s Wall. Tempus, 2001. ISBN 0-7524-1913-7.

Map links
Birdoswald – Streetmap
Birdoswald – Google Maps satellite image

Note for readers of Paths of Exile
I based the (fictional) warlord’s hall at Navio Roman Fort (modern Brough, Derbyshire) in Paths of Exile on the second of the post-Roman timber halls excavated at Birdoswald. There is no evidence that Navio fort was occupied by a local warlord in 605/606 (nor is there any evidence that it wasn’t).


tenthmedieval said...

Nice and careful post as ever, Carla! I just wanted to add to this:

The size of the halls implies that whoever ordered their construction controlled substantial resources of materials and manpower. It’s a reasonable inference that this was a local or regional ruler.

I would say, further, that reoccupying a major fort is the kind of thing that no local ruler worth his salt would be happy with someone else doing, so whether or not the person so doing was such a ruler, he or she was probably setting out to be one...

Gabriele C. said...

Germanic village migration counts 30 years, but those timber buildings had no stone foundations. And it was not only the buildings falling into disrepair, but the arable and grazing grounds no longer rendering enough result. So the whole village would pack up and move on, usually a few kilometres. It's assumed that they partly deconstructed the buildings and used those timbers still intact. I guess they'll have lived in tents or simple huts until the new houses were finished - those migrations must have taken place during summer.

Carla said...

Tenthmedieval - thank you. That reminds me of Ida fortifying Bamburgh, which was presumably part of a foundation story about the origins of Bernicia, and would be consistent with your comment. If you buy the theory about a sixth-century attempt to recreate the command of the old Dux Britanniarum as an integrated entity, then I suppose Birdoswald might be seen as a component of that overall command rather than as a power base in its own right, but even so the commander of the reoccupied fort must still have been de facto the boss in his local area, even if he was theoretically subordinate to a high command in York.

Gabriele - earth-fast timber posts do rot quite quickly. I've seen a suggestion somewhere (think it was in an article about the Iron Age) that it was convenient for timber buildings to last about 30 years as that meant each new generation built itself a new house. Something similar might have applied to the Germanic village migrations. Did the arable and grazing lands recover after a while, so the village could end up moving back onto lands it had vacated several generations ago? It would be possible to live in something like covered wagons for a while in the summer whilst building a new village - something like a summer caravan park :-)

Gabriele C. said...

Carla, you know it's difficult to trace remains of timber and earth structures in a heavily populated country, but a circular pattern has been suggested for a few of those. The other pattern was to follow a river - that can be demonstrated in case of the migration of the Goths by finds in present day Poland; they went up the river Wisla (and others) a few miles every generation and would eventually reach the Black Sea. In that case it was a whole bunch of smaller group settlements that seem to have migrated more or less at the same time. There's still a lot of work to be done.

The worft settlements on the German coastlines followed along the coast. For some reason the people stuck to the complicated construction of large earthen hills to put their houses on, and a system of dykes, instead of moving further inland. Probably liked fish a lot. :)

The Fantasizer said...

I jst came upon your blog and i love it, though I do have a suggestion perhaps you could post cover art alongside the books you are reviewing that would certainly brighten up your blog a little bit.
Anyway I dont wanna sound critical, your blogs great as it is.

Carla said...

Gabriele - are those related to the settlements I know as terpen? Low artificial mounds with a village on top. If you can catch fish and collect shellfish a coastal environment can be very rich, a lot easier to get food from than agriculture. Probably well worth the effort of building something to live on, assuming you like fish, of course :-) Surge tides must have been bad news, though.

The Fantasizer - hello and welcome! This particular post isn't a book review, so no cover art available. Sometimes I post diagrams or photographs.

Gabriele C. said...

Sounds like the same thing. The North Sea coast in Germany and the Netherlands, as well as parts of the Baltic Sea coast, are very flat, and if you want some protection from floods, you have to put your houses on artificial hills, or build drainage systems and dykes. There are still mounds today, the Halligs, and dykes pretty much everywhere along the coast. Floods can still be bad news, modern floodgates nonewithstanding, like the big one in Hamburg in 1961. And the tunnel under the Elbe in Hamburg gets flooded on a somewhat regular basis.

Rick said...

Belated comment! I wonder about the final (?) wooden building that was relocated somewhat from an earlier one, and no longer on top of the Roman granary foundations. Which might suggest a long enough period of disuse that the foundation had been buried. Otherwise why not re-use the handy existing granary foundation, which was about the right size.

But it is equally possible that the Roman foundations simply no longer fit the land use pattern, and the guy in charge said 'Tear down that building and relocate it to leave room for Whatever.'

I suppose Birdoswald might be seen as a component of that overall command rather than as a power base in its own right

This was historically the great challenge for extensive polities - whoever you entrust with the keys to a local fortress had better be trustworthy, or you just created a local warlord.

There are times and places when former fortresses are merely impressive buildings, but Britain before the 18th century was never one of them. Think of the Parliamentary 'slightings' in your Civil War.

Here's a sadly romantic thought: Perhaps what the Arthurian story really conceals is that Camlann and even Mount Badon didn't really matter, because by then the central government's authority had already been usurped by local commanders.

The sad romance came later, the Welsh being known masters of jive. At the time it might have been all rather graceful, an Anglo/Welsh version of the wonderful colonial Spanish, Obedezco pero no cumplo, 'I obey, but I do not comply.'

Carla said...

Gabriele - not so dissimilar to parts of the east Anglian coast, where 5m elevation counts as a hill and there are quite a lot of dykes along the coast and estuaries. I don't think this side of the North Sea goes in for terpen, though.

Rick - Never too late! The second wooden building is the last in the sequence on the north granary site; it wasn't the final building in the fort, as there is at least a medieval tower house, an early modern bastle house and the 17th/18th century farmhouse. The stone post pads for the second building had been laid in trenches cut through the floor of the granary, so I reckon the builders knew perfectly well that the granary was there. Shifting the building footprint as they did gets the new building to line up with the still-open portal of the west gate. The gate had originally been a double portal and the original granary was aligned accordingly, then the south portal of the gate was blocked up during the Roman period. The second timber building aligns with the edge of the remaining portal. I would say its siting was a deliberate decision - the guy in charge said "I want my hall right by the gate, so see to it".

Local commanders and control thereof is a perennial problem. The Western Roman Empire must have got pretty fed up with legionary commanders in Britain using the troops under their local command to form breakaway empires or to make a grab for the top job. On a smaller scale, the sort of local warlord you describe is consistent with fragmentation of Roman Britain into little kingdoms (maybe partly based on civitas districts as sort of city-states), which may well underlie the conflicts in the Arthurian legends. You can cast Arthur, in sadly romantic vein, as a sort of fifth/sixth century Llewellyn the Last, trying to unite a quarrelling bunch of local rulers who were all more interested in grabbing what they could from their neighbours (including the central authority) than co-operating. Gildas is consistent with this. Camlann is in the Triads as one of the Three Futile Battles, which may suggest that even in sad romance its outcome didn't matter much. We've discussed before the possibility that early medieval/post-Roman Britain might have been ungovernable by anybody.

Gabriele C. said...

Carla, one of the reasons Emperor Honorius told the Romans in Britain they had to look after themselves now - after Constantine III had marched off with most of the army to kick Honny out - in 410 AD was indeed the fact that the Roman Empire had its fill of a place that kept breeding ursurpers pretty much since the early 3rd century.

Then the remaining Romans and romanised Britons did what the rest of the empire did as well: hire German mercenaries. Problem is that those kept staying in the long run. *waves to Odovacar who sent the last Roman emperor packing and took the job himself* :)

Carla said...

Gabriele - absolutely. Marcus Didius Falco's opinion of Britain may well have been widely shared :-)

Rick said...

As I recall, Odovacar politely packaged up the imperial regalia and sent it to the Eastern emperor Zeno in Constantinople, saying that a separate western colleague was no longer required. Zeno could henceforth exercise undivided imperial authority, and Odovacar kindly offered to administer Italy in Zeno's name, complete with Zeno's image on the coins.

How could Zeno turn down a gracious offer like that?

Regarding the building position, I'd forgotten your point about it lining up with the gate, which sufficiently explains the relocation.

Gildas is indeed consistent with the picture of effective power having slipped away from the center to local leaders. And we talked some time ago about the disappearance of coinage and the problems that posed for taxation.

Colin said...

Hi Carla,
Will you be up by the Wall at the weekend when the torches light up all the 83 miles? I know that illuminating the wall sounds very much 20th century, especially as gas burners are being used. But when viwed from afar as the day darkens into night i hope that it will be a magical evening.
Many thanks for the article on Birdoswald...our limited experience of this period in time is more based up in the Cheviots and the Till plain.

All the best


Carla said...

Rick - Yes, that was an offer not easily refused :-)

Colin - Hello and welcome! That's a spectacular picture of Hadrian's Wall on the front page of your site. I'm afraid I won't be in the area for the lighting up - I hope it's a spectacular show for you.