Inchtuthil- The Fortress on the Wing?

Welcome to my Monday Musings!

I've taken some time off my writing in progress to jot down some of my research on the fabulous Legionary Fortress at Inchtuthil in Perthshire, Scotland. This blog post is also intended for the shared blog posts associated with the Historical Writers' Forum where you'll find a huge range of eras  and subjects covered by the group of historical authors that I'm delighted to be a part of.   

Inchtuthil - Pinnata Castra, The Fortress on the Wing!

Mapmaking details of Claudius Ptolemaeus (Ptolemy), writing around A.D. 120-150, name an Ancient Roman Fortress in Caledonia as Pinnata Castra. This is translated as ‘the fortress on the wing’. The exact position of this fortress is hard to discern since the medieval map created from Ptolemy’s assembled references is oddly skewed with Scotland appearing at right angles to the rest of mainland Britain. 

No large legionary fortress has ever been identified near the Moray Coast where it is sited according to the medieval version made using Ptolemy’s projections. Ptolemy also names a fort as Victoria, some historians believing that one to have been named after the Battle of Mons Graupius as mentioned by the Ancient Roman writer Cornelius Tacitus - the name Victoria often conferred after a notable Roman victory over enemy tribes. However, there has never been a large fortress identified near the Victoria location as detailed by Ptolemy.  

It, therefore, makes sense that the huge fortress (21 ha/50+ acres) positively identified at a site named Inchtuthil in Perthshire was the one Ptolemy calls Pinnata Castra since it’s the only large legionary-sized fortress ever identified in northern Caledonia. Or it may be that Victoria was built further north at the Inchtuthil location and mistakenly plotted on the map!  I chose to name Inchtuthil as Pinnata Castra in my Celtic Fervour Saga series since I like the idea of the fortress being on the wing, essentially at the edge of the fortifications that were built north of the Forth/ Clyde line.  

At Inchtuthil there's evidence of a legionary fortress likely to have been mainly built and garrisoned by the Twentieth Legion (Legio XX Valeria Victrix). Built to garrison as many as 6000 men (a full legion plus additional specialist troops), its position was highly strategic and placed on a natural plateau with outstanding views over the surrounding countryside. On the north bank of the River Tay, it had access to sufficient water supplies and it was in the best place to monitor one of the main natural routes into the Caledonian highlands. The River Tay was also a navigable inland waterway which was ideal for small vessels of the Classis Britannica (Roman Navy) to ferry in essential supplies from southern supply bases. The building work at Inchtuthil is thought to have begun around A.D. 82/83 on the orders of Gnaeus Iulius Agricola, Commander of the Britannic armies and Governor of the province of Britannia between c. A.D. 77 - 84. Inchtuthil was not a long-lived fortress, though, since it was probably dismantled and evacuated sometime around A.D. 87 ‑ more about this at the end of this post.

Since General Agricola was familiar with the creation of the Eboracum Roman Fortress (York), while he was serving as the Commander of the Twentieth Legion, some historians believe he chose the site and layout of Inchtuthil using prior knowledge of the successful fortress at Eboracum. The fortress at Eboracum was sited close to the navigable inland waters of the Rivers Ouse and Foss and this may have influenced Agricola's decision to choose the location for his northern 'powerhouse' fortress. 

The operations of the small vessels of Agricola’s Roman Navy were crucial elements in the success of the Caledonian campaigns. It’s likely that only smaller vessels of Agricola's fleet could have navigated up the River Tay but they would have played a regular role in supplying the north of Caledonia. It's always worth mentioning that Agricola was innovative in using his Classis Britannica (Roman Navy) for more than in a supply role – he also appears to have given the fully armoured mariners an aggressive role in subduing the natives who lived close to the eastern coastline of Northern Britannia. This seems to account for the fact that coastal forts or fortlets in north-east Caledonia are quite rare.

Though the only legionary fortress in northern Caledonia, Inchtuthil was part of a line of strategic defence structures intended to control movement of the natives between the highlands and the fertile plains of current-day Fife, Tayside, Aberdeenshire and Moray. Experts of Roman Scotland refer to two main lines of defences built during the Agricolan invasions as the Glen Blocker Forts (Drumquhassle to Cardean) and the Gask Ridge defences (Doune to Bertha) which were used to encircle the highland massif. (N.B.Use the blog archive to access other posts about these installations). 

South of the Gask Ridge, Agricola also had sufficient defences controlling the Forth/ Clyde line which effectively monitored the southern accesses to the highlands.

The fortress at Inchtuthil was the lynchpin of all of these highland defences. Agricola’s aim was probably to use this fortress as a supply base for all future operations north of the Central Belt of Scotland, there being many tribes and territory still to subdue in the far north.

Since the site of the fortress was never built over in ensuing centuries after the Roman occupation, and remained pastureland, it allowed for thorough archaeological excavation (Richmond 1952-1965), though some small-scale investigation of the site had been undertaken in the very early 20th century. Because of its location and undisturbed condition, Inchtuthil is the only site across the Roman Empire that provides the best complete plan of a legionary fortress.

Inchtuthil’s main barrack accommodation blocks (64) were built close to the perimeter but behind the intervallum – the space left free inside the rampart walls the distance of it being set to be the widest extent that missiles from outside the walls could fall. The intervallum space was probably also used for mustering and rapid deployment of troops, and used regularly for drills. Larger than normal workshops (N) were created for manufacturing all of the iron requirements needed for a permanent stay in northern Caledonia (for tools, weapons, and fort building components like nails and brackets). A very sizeable hospital was also built. An outside rectangle of small rooms faced a smaller rectangle of rooms, the rows separated by a walkway (K). To the interior lay an open courtyard.

 

courtesy of SCRAN/ RCahMS

The timber walls of the above buildings alone had an approximate perimeter of 7 miles so the wood cut to create the whole fort would have denuded forests for miles all around the area. It’s estimated that building such a large installation would have taken a few years, the troops living in tented accommodation in the temporary camps situated outside the fortress till the barrack buildings were completed.

There seems to have been construction priorities at Inchtuthil. Some of the expected buildings were never completed and others were unexpectedly small. Generally in a fortress of this size there would have been a sizeable headquarters administration block (P - principia) and a generously-sized building to quarter the legionary commander (praetorium) built in the centre of the fortress behind the via principalis – the main road that ran transverse between slightly offset side gate entrances. At Inchtuthil, there is an unusually small principia and no evidence that a praetorium was ever constructed on the empty space that was laid out for it. This meant a fairly empty centre to the fortress. And some of the Tribune's officer accommodation wasn't completed.

There's evidence for 5 massive granaries, designed to hold months, perhaps even years, worth of grain. It's possible their size was designed to accommodate grain 'payments' from the locals -  although there wasn't really all that much fertile soil for grain crops in north-east Scotland. The locals mostly grew oats and barley, the latter being a ration apparently hated by the Roman troops. It's possible that space for a further 6th granary was laid out but not used. Agricola's concept of Inchtuthil being a huge supply fortress for an offensive further north at some future date was sound, especially in the amount of food stocks that were necessary to feed his four Britannic legions spread throughout the whole island of Britannia. The general troop diet was mainly a wheat-based one - bread and a form of brose/ porridge, and hard tack biscuits when on campaign - but it took tons of grain to feed those men. 

The small principia functioned as the headquarters building, the records store, the place where justice was meted out and where religious ceremonies took place. The aedes - the rear section - would have housed the precious emblems and standards of the legion, the emperor’s image, and altars for worship with the strong room beneath for storage of the legion pay-chests. There may have been a plan for this building to have been enlarged at some point but that never happened. Outside the fortress walls there was a temporary camp officers' compound which seems to have been used during most of the construction phase. It may be that the principia was small because official business was still being conducted from the officers' compound. Interestingly, the remains of a small personal bathhouse were found near that senior staff compound. 

General Agricola was recalled back to Rome in early A.D. 85 but it's not clear who his successor was. It may have been G. Sallustius Lucullus [executed in A.D 94 and there's a nice story for this for another post] but, if him, his tenure as Governor of Britannia would have been incredibly long. By the time Agricola was recalled to Rome, and his almost unparalleled 7-year tenure  ended, Emperor Domitian had already been withdrawing troops from Britannia for some years. Caledonia was seriously undermanned when Agricola left and the troops stretched too thinly across the island of Britain to maintain control over all of the areas invaded. Inchtuthil may have been Agricola's 'pet project', built for sound reasons when in aggressive invasion mode but Agricola's successor may not have had the authority from Domitian to continue to man the northern areas of Caledonia, or even the will to continue with Agricola's ambitious plans. It's not clear when all of the troops retreated from the north and were deployed in southern Britannia after Agricola left Caledonia, but most historians think the troops withdrew down to around Trimontium (Melrose on the Scottish Borders) by the late A.D. 80s. 

General Agricola- Wikimedia Commons 

The fortress at Inchtuthil was probably dismantled and evacuated around A.D. 87 (coin evidence indicates before A.D. 90), the likeliest reason being that Emperor Domitian needed more troops because he was heavily involved in war in Moesia (Balkans)/ and Dacia . Domitian recalled troops of the Legio II Adiutrix Pia Fidelis from Britannia to stem the unrest. This left the northern areas of Caledonia undermanned. It's thought that most of the troops of the Legio XX moved south to man the base at Deva Victrix (Chester) when it was evacuated by the Legio II Adiutrix Pia Fidelis. 

The dismantling process at Inchtuthil was an organised one. If there were elements in the fortress that could be used elsewhere in Britannia, or even across the wider Roman Empire, they would have been packed up and carted off during the withdrawal. Items unwanted like already chipped pottery, unrepaired fittings tended to be consigned to the rubbish pits. In general, nothing was left that the enemy could use to their advantage. Since iron seems to have been the most prized commodity in Late Iron-Age society in Caledonia, probably even more esteemed than gold or silver, it is highly unusual that a massive amount of iron was left at Inchtuthil. Naturally the iron stocks weren’t just left lying around! 

Since the workshops were up and producing early in its history, it’s thought that there were huge stocks of nails ready and waiting for major fort building further north, the Caledonian campaigns expected to continue for some time. Nails of varying sizes, from very small to the huge spikes that were used to connect thick upright posts, were purposely packed into a deep pit and covered over before the fortress buildings were set alight prior to the evacuation of Inchtuthil, a normal procedure when abandoning a fortress. It seems as though the almost one million nails (875,400), iron wheel rims and fittings - upwards of 10 tons worth - were impossible to cart away and this was an attempt to deny the locals from finding them and melting them down to make valuable weapons.

When Richmond excavated the site at Inchtuthil in 1960 it must have been a huge thrill to find this amazing treasure chest beneath the ground. When the pit was first dug, they found a large slab of iron, and under the slab which was in fact multitudes of fused iron nails, they found the cache of intact unused nails. Collections of nails were gifted to museums, some sold off to interested buyers and I read somewhere that some of the remainder ended up in a steelworks in the Central Belt of Scotland. Atomic scientists have studied some of the nails to estimate corrosion effects on barrels of nuclear waste. Click the link below to see a photograph of those amazing nails! 

https://www.scran.ac.uk/packs/exhibitions/learning_materials/webs/56/Inch.htm

I’m currently writing about this amazing fortress in Book 5 of my Celtic Fervour Saga series. My character Agricola has been summoned back to Rome from his campaigns in what is now north Aberdeenshire and Moray. Agricola is determined to see the progress at Inchtuthil on his way southwards since he knows it’s the pinnacle of his achievements in Caledonia.

Happy Reading.

Slainthe!