Banks and Ditches Across The Tamar

For the uninitiated, The Tamar is the demarcation line between Devon and Cornwall. This side of the river everyone is civilised. That side people often have a third eye and talk a different langauge. At least those who haven't retired there - which leaves scant few with ocular distrurbancies.
The Tamar also marks the boundary of Roman intervention in Britain. Let's re-phrase that. Tradition has it that the Romans did not get past the Tamar into Cornwall. Ego dictates that the Romans couldn't conquer the territory. Sense has it that there wasn't any place called Cornwall two thousand years ago and that what we now know as that county is a mixture of indigenous Britons, Irish settlers, emmets and grockles.
Unfortunately, the Romans weren't much for tradition and had little respect for the ego; turns out that they did get over the Tamar and there are forts enough to testify to the fact. Two of those forts - and let's note that these are the forts that have been discovered, as opposed to those forts that did in fact exist - two of those forts, at Restormel and at Nanstallon, are situated within a matter of miles from each other, but were built on two , unconnected river estuaries, the Camel and the Fowey. Sitting in between, a modern monster hiding a potential ancient jewel, is Bodmin. (Or Baaardmin, if you have a third eye).
The third fort, discovered soon after Restormel, sits above Calstock on the Tamar - the wrong side of the Tamar - and whilst the first two are comparatively small at between 80 and 100 metres down one side, the Calstock fort is almost twice the size, at 160m by 170m. It's not just the size that's important though. The site, which easily surrounds the Church and its environs, also appears to incorporate the still surviving road that leads down to Calstock proper. 
As yet, the archaeologists responsible for the dig have yet to publish their results and if past experience is anything to go by, we may have to wait a very long time for that to happen. However, if there's any connection between the three forts, it may be concerned with the brevity of their use. Nanstallon certainly was occupied for just a couple of decades in the first century AD and because of the geographic connection with Restormel, it's likely that both establishments were part of the same strategic development.
Perhaps though the size of the Calstock fort and the characteristics of its construction may indicate a longer life. Certainly, there is medieval documentary evidence of an 'old fort' at Calstock which would suggest that the banks and ditches were prominent enough to have survived for more than a millenia.
The other intriguing aspect of the Calstock fort is that it doesn't fit in with the traditional view on Roman incursions into the South West peninsular. A brief chain of marching camps to the north of Dartmoor, have led to the conclusion that soon after the AD43 invasion (soon perhaps meaning decades), the legionary force at Exeter pushed round Dartmoor, crossed the Tamar somewhere and moved into what became Cornwall. The Bodmin forts fit in with that notion quite well. However the Calstock fort is a long way south from any projected route from north of the moors and may imply a southern route or perhaps a second advancing column.
Yet all that speculation is centred on the assumption of a military campaign. That all three forts reside on river systems - three different rivers note - could lead to the conclusion that there was no heroic marching campaign at all and that the structures were naval stations used to stock mined materials - tin or silver - before they were shipped back to somewhere in the Empire.
Now, I promise we'll go out in the next few days and take some piccies ...