What we know about IOC is not limited to theory or systematic research. IOC structures have existed perhaps as long as organized society itself. Prehistoric clans cooperated in the hunt, as we can see from the practices of stone-age societies surviving today, and tribes formed alliances and federations in war. Hierarchical coordination embraced vast empires in bronze age and classical times, from the master planning of cities in the Indus valley, to the ramified bureaucracies of Egypt and Babylon.