Originally Posted by
Ninthace
The Roman Empire had different northern boundaries at different times. I seem to remember that they settled on the line of Hadrian's Wall on the grounds anything north of there was not worth the effort. A sort of cost/benefit frontier based on bean counting.
There is also the small matter of the Antonine Wall, built across the central belt from the Firth of Clyde to the Firth of Forth. There were certainly excursions north of this, but by the eastern route (or by sea), in the same way the Borders/Northern England have the east, central and west Marches. The Highland Line (north of which is LFA14 to you pilots) created a huge physical barrier. One need only stand on the ramparts of Stirling Castle to appreciate that an army on foot must pass the bottle neck created by the impenetrable Flanders Moss and the River Forth, which is why the castle was built there. A little stream called the Bannock Burn meanders across in front of it. As the Scots proved many times, defending north of the bottle neck from huge armies was relatively straight forward, subject to internal politics. (Nothing changes!). Most tourists do the Edinburgh Castle thing. Stirling is far more impressive.