#A2ZChallenge G is for the #Gask Ridge and the Glen Blockers

G is for the Gask Ridge and Glen Blockers

Theme: Ancient Roman Scotland during the Flavian era
(Grab a coffee- today's post is along one!) 

What's the Gask Ridge? And what are Glen Blockers? Fabulous questions about fascinating installations. 

They each refer to a line of fortifications originally built during the Flavian military occupation of the Stirlingshire, Fife, Perthshire, Tayside and Angus areas of Scotland. When the Ancient Roman legions invaded the territorial lands north of the rivers they named the Clota (Clyde) and the Bodotria (Forth), they found flatter ground heading north-eastwards, though most of the rest to the west and north was mountainous.

Copyright -  Nancy Jardine

Campaigning in mountainous territory wasn’t something the Ancient Roman army would have shied away from since the legions had plenty of experience in continental Europe. 

General Gnaeus Iulius Agricola, Commander of the Britannic armies and Governor of Britannia (consul), had personal experience of campaigning in the hill regions of northern Britannia (Yorkshire, Cumbria, Northumberland) before he marched further north into Caledonia, so he would not necessarily have been too concerned about mountain campaigning. 

My home-made map indicates some of the wooden forts and fortlets that were situated on the two lines of defences, ones which I have focused on during my studies, or for using during my presentations on Roman Scotland - but there were many others not on that map. The line closest to the mountains at the west, beginning with Drumquhassle and ending at Inchtuthil, is often named as the 'Glen Blocker forts', or sometimes as the 'Highland Line'. 
(I'll be writing more about the Glen Blockers and especially Inchtuthil as my 'I' letter during this #A2ZChallenge)

Click HERE for much more detailed maps. (The Roman Gask Project)

The line of forts which is to the west of the lower hills in Fife and into Tayside, including Ardoch and Bertha, are part of the line of installations known as the Gask Ridge or Gask Frontier, though the Gask Ridge more likely begins at Camelon (near Falkirk). For the last two decades, a lot of time and effort has been put into identifying and excavating a much larger number of fortlets and smaller watchtowers which follow the Gask Ridge line. Each tiny dot on the map below represents the small watchtowers that have so far been identified, and there's still hope of more to come north of Midgate fortlet.

Copyright - Nancy Jardine

As well as the substantial forts of Ardoch, Strageath and Bertha - all known for many decades to be Roman forts - Doune Fort was discovered by aerial reconnaissance in 1983. There were earlier possibilities of Roman activity in the area but they hadn't been substantiated till the post-1983 excavations. Interestingly, the Roman fort at Doune sits on what is locally named 'Castle Hill', yet the well-known medieval Doune Castle is located on lower ground to the south-east.(Roman name for a fort is castellum). The site at Doune Fort currently has school buildings and housing on it, so excavation was restricted. A coin of Vespasian was found nearby which helps to date the area as initially of Flavian occupation, though full excavation reports of Doune Fort have never been available. 

In between the major forts on the Gask Ridge are a couple of smaller forts and a series of watchtowers sited at fairly regular distances apart  in effective vantage points, which must have provided good knowledge of movements around the area, of natives and of Roman troops. Across the whole line of Gask Ridge fortifications, initially built by Flavian troops, are later uses during the Antonine and Severan eras.

copyright - Nancy Jardine

Intriguingly, little effort seems to have been made by the various Roman occupations to monitor activity in and out of the Fife area: no permanent Roman installations have ever been found to the east of the Gask Ridge. There were a few temporary camps but they do not seem to have been converted into permanent wooden forts or watchtowers. This lack of fortifications leads some experts to a viewpoint that the Venicones tribes who lived there had allied themselves to Rome and needed no monitoring - but this theory cannot yet be proved. (tribal names as per Ptolemy map data of c. A.D. 120-150)

The generally poorer weather conditions in northern barbarian territory of Britannia wouldn’t necessarily have fazed the Romans. However, mountainous regions tended to need plenty of manpower since a forward invasion into them wasn’t as logistically simple as striding forward in relatively flat countryside. The mountain range we now call the Grampians has many access points – many glen openings. This would have meant multiple opportunities for a horde of avenging locals to spill out from to attack invasion forces, as much as opportunities for penetration into the mountains by Ancient Roman forces on the offence. 

General Gnaeus Iulius Agricola’s campaign strategies are not really known but marching his full legionary and auxiliary forces, of possibly upwards of twenty thousand soldiers, into the Grampian Mountains in search of the Caledonian enemy doesn’t seem to have been what he did. Though, to date, there is no evidence to prove, or disprove, that possibility. But there is evidence of him building temporary marching camps on the flatter plains areas, northwards of Inchtuthil Legionary Fortress, all the way to the Moray Firth, some of those temporary camps having been transitioned into wooden forts and fortlets in the territory south of the current city of Aberdeen.

Copyright - Nancy Jardine

A big question which causes some controversy amongst historians of the era is  - Exactly when were the more permanent wooden defences built, those that lie to the south of Aberdeen? Were they constructed systematically during the protracted Caledonia campaigns as the legions tramped northwards, to ensure that no native attack from the mountains could surprise the Roman army, and the forts and watchtowers were for defensive reasons? 

The Ancient Roman writer Cornelius Tacitus wrote that Agricola marched his men northwards into Caledonia where the Roman troops confronted the Caledonians and their amassed allies in a pitched battle Tacitus named as Mons Graupius (Graupian Mountain). In Tacitus’ work named ‘De vita et moribus Iuilii Agricolae', usually named 'The Agricola’, he gives detailed battle plans for Mons Graupius but no conclusive geographical pointers for the location. Many sites have been postulated for this battle, but no evidence has yet been found on the ground.

Some historians have put forward the theories that Agricola built the Highland Line of defences (also named Glen Blocker forts), and the line of defences named the Gask Ridge, after Mons Graupius. That theory supports the idea that as Agricola’s armies retreated southwards, post battle, the building of the fort and fortlets was to defend and maintain control over territory already won. That theory might work, for me, if the battle site was somewhere south of the current city of Aberdeen and, if after the battle, Agricola retreated his forces southwards without venturing into more northerly uncharted territory.

 Nancy Jardine

However, the ground evidence indicates that’s not what Agricola did, since there’s a line of temporary marching camps almost all the way to the Moray Firth near Inverness - yet none of those appear to have been converted into wooden forts or fortlets (apart from a couple of possibilities around the Moray Firth area, which may have been constructed by Agricolan auxiliary seaborne invasion forces).   

If battle had been won by the Romans south of the current city of Aberdeen, would Agricola have been confident enough to march his troops northwards all the way to the Moray Firth in the belief that he would have gone unchallenged by the surviving natives (some 20,000 according to Tacitus) who could have spilled out towards Agricola’s temporary camps from more northerly glen openings ,of which there are quite a few?

From the site of the Durno camp looking over towards Bennachie   - Nancy Jardine 

Whatever the truth of the timing of the building of the fortifications, it seems, to me, that Agricola had plenty of forewarning of what the mountainous terrain was like to the west; from during his own early summer campaigning seasons c. A.D. 78-80. He may also, perhaps, have even had exploratory knowledge from when Bolanus, Cerialis and Frontinus were Governors of Britannia before his own consulship - if some of their troops (exploratores) had advanced into Caledonia.

Interested amateurs like me, and historians, can sadly only guess and make educated deductions. I, personally, favour the theory that the battlegrounds of Mons Graupius are by the hill range of Bennachie in the Garioch area of Aberdeenshire, a location that has gained much favour since c. 1976 when a huge marching camp was discovered by aerial photography at Durno, on the opposite side of the valley from Bennachie. The Durno camp is the biggest in northern Scotland at c. 58 hectares. The big question not certain yet about Durno is if it is mainly a Severan camp, or did Emperor Severus use it during his campaigns because the site had already been constructed by Agricolan forces? During Severus' Caledonia campaigns of c. A.D. 208-210, he re-used, and adapted, plenty of installations built in Agricoland and Antonine eras.

Let's head back south again to the Gask Ridge and Glen Blocker forts and to the question of manning all of the installations during Agricola's northern campaigning. I read (somewhere) that a very rough estimate for space needed for auxiliaries went something like 1 hectare (ha) per cohort of  c.500 men, though mounted units required more space per horse and rider than infantry.

• Watchtowers: they may only have been garrisoned on a daily daily basis,or is shifts,  by a single contubernium group of 8 soldiers. 
• Fortlets- manned by possibly up to a half-cohort, some 200 men
• Small Forts - somewhere between 1 and 2 cohorts, up to 1000 men as in the fort at Cargill
• Larger Forts - around 2000 men, as at Bertha
• Fortress- Inchtuthil was intended as a legionary fortress of some 5000 men

When he assumed the consulship of Britannia in c. A.D.77, Agricola had 4 legions based in Britannia at his behest. Tacitus wrote that during the battle of Mons Graupius soldiers of the Legio II Adiutrix, Legio IX  Hispana and Legio XX Valeria Victrix were present. This means the Legio II Augusta were manning the rest of Britannia during that time (though more likely what we now term England rather than southern Scotland, since the southern Scottish forts have evidence from units that probably weren't from the Legio II Augusta). Tacitus also states that Agricola was able to raise new vexillations from varying places across the empire, including southern Britannia, to aid his campaign though it's unknown exactly how many were in the additional 'specially formed' units.

I've seen varying estimates of Agricolan forces based on A) Tacitus' information of the battle of Mons Graupius and B)on knowledge of where all of the other 26 (ish) legions were stationed around the Roman Empire at this time. The estimates for Agricola's Caledonian campaigns run something like 18 - 25 thousand soldiers, comprised of legionary forces and auxiliary units - the auxiliaries much more numerous.

If that is how it was for Agricola, then looking at the need for manning installations south of Aberdeen, it seems possible that Agricola could have advanced north with the bulk of his legions, though the installations left to the south of him may well have been seriously undermanned. Tacitus specifically wrote that the Legio IX Hispana was vulnerable since Domitian had acquired men for Continental campaigns c. A.D. 82 and 83. The soldiers whose duty was to monitor the Glen Blocker installations and those on the Gask Ridge must have born a heavy responsibility, to warn the main invasion force of any imminent attack from a southerly or westerly location. 

That said, the Ancient Roman legions were such a well-drilled force that news was carried very efficiently, and very effectively via signalling systems, from watchtower to nearby fort, and thence onward to the more major installations. From there dispatch riders could easily take news north and south.

There are plenty of questions about when the Gask Ridge and the Glen Blocker/ Highland Line forts were actually built, but no definitive answers. My deduction is that although Agricola's legions lacked the numbers he ideally wanted, I think the Gask Ridge forts and associated watchtowers were built either when the main legionary forces were encamped in that area, or just after the main legions tramped northwards. That would ensure no pincer attack came from the Venicones over the low hills from an easterly direction. If the Glen Blocker/ Highland Line was being simultaneously established, then attack was less likely on the main invasion forces as they marched north. Tacitus does mention an attack which almost wiped out the Legio IX, though Agricola saved the day himself by arriving in time! Now where had he been beforehand to manage that? It's a fine question that I have no answer to but it seems he was arriving FROM the south or the west.

I'm less sure of when the Glen Blocker forts were established. I lean towards the opinion that Agricola already had their building in the pipeline during his campaigns of 82 and 83, his 5th and 6th summer campaigns, if I assume that he was in Aberdeenshire during his 7th campaign  in A.D. 84, Mons Graupius happening late in the summer/autumn of 84. Or, the planning and building of the Glen Blocker Forts was maybe even earlier, since he may have learned how formidable it would be if the tribes rallied in the Caledonian mountains for battle and descended on his troops from more than one glen openings. 

When all is said and done, as the Governor of Britannia Agricola was responsible for the peace and productivity of all lands to the south of wherever he was campaigning in the long island stretch that was Britannia. That must have been an immense task to oversee.  In Agricola's Bane, Book 4 of my Celtic Fervour Series (an Iron-Age tribal clan saga), Agricola is highly frustrated during his post-battle tramp to the Moray Firth because his legions are spread far too thin...and worse than that... Emperor Domitian is constantly clawing back more and more of the Britannic units to aid those fighting the Chatii in Lower Germania! 

What theory would you put forward for why and when the Gask Ridge was first constructed? 

Slainthe! 

I've found this an excellent source for my Roman Scotland studies. (Though I have many others to dip into as well. )
Rome's First Frontier
The Flavian Occupation of Northern Scotland
by D.J. Woolliscroft and B. Hoffmann