The old Duchy of Saxon began to split up in the 15th Century, because law said that all sons should inherit. All of the sons of a Saxon duke had the title of "Duke", sometimes brothers ruled the territory together, and sometimes they divided it up between them. Some of the Ernestine duchies stayed independent until 1918. The nearby royal houses of Reuss and Schwarzburg also divided up their territory, so Thuringia was a tangle of little states, exclaves and enclaves from the late 15th Century until the early 20th Century.