The Economics of Owning a Medieval Watermill

Magna Carta has 63 clauses. One of them orders every fish weir torn out of England's rivers — because weirs were part of mill dams, and mills had already made enough enemies to get written into the most famous document in English history. We build one from scratch: the imported millstones, the illegal hand-mills the abbot of St Albans confiscated and paved his floor with (until the 1381 revolt dug it back up), the toll nobody could legally avoid, and the reason the miller almost never got as rich as the lord who owned him. Then we find out who actually profited from a resource that never needed a harvest to keep producing.