What is a “commenda” contract in medieval Mediterranean commerce?

The story behind the answer

In medieval Mediterranean commerce, a commenda paired a sedentary investor (commendator) who supplied capital with a traveling merchant (tractator) who conducted a voyage and traded on the investor’s behalf; profits were shared by prior agreement (often three parts to the investor, one to the agent), and the investor’s liability was limited to the stake. This arrangement spread from Islamic qirad/mudaraba models into Italian cities like Genoa and Venice, fueling long-distance trade while skirting usury bans by paying profit shares rather than interest. It differed from sea loans (bottomry/respondentia) secured by ship or cargo, from ship co-ownership, and from monopoly grants.