Very simplistically, the era of Rome can be split into the time of the Republic with its expansion around the Mediterranean and the Imperial period with its civil wars and northern expansion. The II/33 Polybian Roman (275-105BC) list captures the height of the Republic when the Roman Legions crushed the Greek cities, Seleucid, and many others.
The II/33 Polybian Roman list offers no choice of units at all so it is very easy to collect. If needed, the army could also be fielded as II/49 Marian Roman (105-25BC) if one ignores some of the visual differences that the Marian reforms would have created.
Cavalry: Two units of Cavalry including the General.
Blades: The main elements are classified at Blades and represent both the Hastati (first line) and Principes (second line) of a traditional Roman Legion
Spears: The Triarii are the wealthy third line of the Roman Legion – classified as Spears in DBA.
Psiloi: Velites are skirmishes with throwing spears that engage the enemy in advance of the Hastati. The Polybian Romans are the last force to use actual “Roman” skirmishes as following Imperial Roman armies usually relied on subjugated troops to fill these roles.