There is a gentleman not too far away (in the Kaskaskia River bottoms near Bartelso IL, for anyone interested) who has built his own fortress over the past 20 or 30 years, by carrying each stone by hand. The outer stone walls are about 6 feet thick, with openings for his cannons. (he owns several Civil War type field guns. I'm assuming they're reproductions, but considering how "eccentric" this fellow is, they may be origionals.) Now and then the farmer neighbor lets him lob rounds out into his field a half mile away.
To get closer to on topic, he built one of his mortars himself. I forget now what kind of steel piece he made it from, but I recall he said it took three days straight on a lathe. Even made his own carriage for it, and sometimes pulls it behind his horse in parades.