First Fort

This is a bit of a strange one.  I had to dig out one of my best magnifying glasses to read the sign these people are holding, "SITE OF NORTHERN BASTION OF FIRST FORT TRIANGULAR IN PLAN 160."  The only thing  I can guess that makes any sense is that the military has seized land for some sort of fortification.  But where?  Some place temperate and green but cold enough in the winter to require heavy coats.  I'm tempted to go with England during the first world war, but there are a lot of other possibilities.

I bought this photo and the next two, clearly from the same source, at an antique store on the way back from a short trip.  There were others which, given the opportunity, I'll buy next time I head out that way.  So, it's a collection tagged Triangular Plan in labels.