Pirates have been around as long as people have used the oceans as trade routes. At the time of the Roman Republic, they became a state-threatening menace, because the expanding Imperium depended on a functioning sea trade like no other empire before.
Around the mid-1st century BC the metropolis of Rome was facing famines because pirates regularly captured the cargo ships with grain from North Africa. Hence in 67 BC, the Senate invested Gnaeus Pompeius Magnus with powers and means to extinguish piracy. This denarius, minted that year, may habe been appropriated to that very purpose.