Around 319BCE, Athens held 21,000 freeborn adult men and 100,000 slaves. Its economy ran in part on slave labour: slave gangs would dig for silver in the mines of Laurion, just south of Athens. The rich made their money by possessing these mines, or by holding other kinds of land or manufactories. The set-up of Athenian politics made it mandatory for these propertied men to sponsor public works. Wealthy citizens were required to fund theatre festivals, to contribute to the building of warships and to underwrite athletic contests.