Classical civilizations built complex global markets trading gold or silver for spices, cloth, wood and weapons, most of which had standards of quality and timeliness. Considering the many hazards of climate, piracy, theft and abuse of military fiat by rulers of kingdoms along the trade routes, it was a major focus of these civilizations to keep markets open and trading in these scarce commodities. Reputation and clearing became central concerns, and the states which could handle them most effectively became very powerful empires, trusted by many peoples to manage and mediate trade and commerce.