Avoiding the obvious comparison of the numbers in most PC parties equalling the lowest division of that law it seems that at least in the Anglo-Saxon period, a relatively small number of men could threaten to topple entire Kingdoms. If it can be argued that the Harnic Kingdoms are more akin to those Kingdoms than the larger, monolithic state of post Norman England, than even relatively small fortresses with a single company of troops can mean the difference between surviving a war and having your entire clan exterminated in such a conflict.
I'd fully agree here in regards to the scale. england at this time probably had a population of double that of Harn, but Harn also has those small kingdoms more similar to Saxon Europe. One difference I think is that Harn seems to be far more "militarized" than most historical kingdoms.
But the other thing - Saxon England did nto have many stone defensive works (castles with a broader definition
Again, it takes a lot of money to build in stone, money, time, and workers.
It's not that the Saxons did not build in stone - but the churches and monastaries were suually what were made of stone, showing that these structures were though to be more permanent and were built more "expensively" out of stone.
Here is an investory of manpower needed to build Dover Castle:
One of these majestic structures could take up to ten years to build. (That's how long it took to construct the impressive Dover Castle). When the Welsh Beaumaris Castle was built the supervising mason (Master James of St. George) presented a synopsis of the workers required and their levels of expertise. He said there were four hundred masons, two thousand workmen with minimal skills, 200 quarrymen, thirty smiths (iron workers) and innumerable carpenters installing things such as floor boards inside the castle. The cost of paying these workers was too high for even a king to afford and their wages were often in arrears.
Much of it was fished by 1216, so the time period seems to fit Harnic Castles. Look at how mush a day you are paying in labor -Lets say 2d for the masons, quarrymen, smiths and maybe 400 carpenters at 4d. 1d for the uskilled labor.
That's about 3,660d per day merely for the labor, not materials, no extra money for the head people in charge of design.
Dover is a big castle, no doubt, but even quartering that you are looking at about 900d per day for labor. AND what makes it even tougher, finding a work force of 700 workman would be tough in population challenged Harn.