Speculatores and Exploratores were the scouts and reconnaissance element of the Roman army. In both the legions and in the praetorian camp, speculatores were initially scouts but became bodyguards, couriers, law-enforcers, and sometimes executioners. Exploratores were tasked to keep watch on enemy movements in the field. Both occupations could require the wearing of 'plain clothes' and may therefore be deemed spies (Occulta speculator/speculatrix). The Roman Empire lasted a very long time and various espionage units, including the infamous frumentarii created by Hadrian to suppress internal dissent, and later the agentes in rebus, came and went throughout its history.