The third line of the Republican Roman army. Veteran spearmen.

The Triarii (Latin singular triarius) was the third standard line of infantry of the Roman Republic's army. Its name is related to the Latin word tres ("three"), ultimately derived from Proto-Indo-European *trei-. When suffering defeat, the first and second lines, the Hastati and Principes, fell back on the Triarii to attempt to reform the line and allow for a counter attack or withdrawal of the other lines.