Around 150 BC the Roman legions adopted a dagger of Spanish origin and from this point forward it was to see almost continued military service until the decline of the Roman Empire.
These daggers had short pointed blades of around nine inches in length and were especially effective at piercing chainmail body armour.
The pugio was favoured as a secondary sidearm to the Roman gladius-short sword and was widespread in its use until the general adoption of the longer spatha-cavalry sword, as the primary Roman sword of the legions around AD 100.
Although examples of pugio after AD100 have not yet been excavated they do seem to reappear by the third century again however it is most unlikely that such a useful secondary sidearm ever really ceased to be carried by the individual Roman soldier.