Late Roman Unit Sizes

[ValentinianVictrix]

Evan wrote:
Their names really say nothing about what kind of troops they were. The Lanciarii were heavy infantry, Legio Palatina; so were the Mattiarii. Both of them were front-line units.

Why would anyone send heavy armed infantry to act as scouts? Doesn’t seem tactically logical. The hastati were missile armed infantry but they also fought close combat. In comparison to the velites, the hastati were heavy armed infantry. In comparison to the principes, the hastati are light-armed infantry. I have not seen any evidence to suggest that the Roman army, and I also mean the Late Roman army did not consist of two troop types. One of them must be more missile armed than the other. The battle of Strasbourg shows this to be so.

The question I am asking is are the Mattiarii armed with the lead weighted dart (Vegetius 2 15)?

I think your unfamiliarity with the Late Roman army shows at this point. There are numerous examples in Ammianus where he describes legionarii and auxilia are sent on special missions and when they do so they are called 'expediti', which Rolfe translates as 'light-armed'. Its clear in one instance that it meant troops taking off their armour and just relying on their shields to defend themselves. Ammianus does mention light troops separate from the legiones and auxilia, and calls them velites, Julian and Libanius called them Psiloi.

The Late Roman unit names are a trap for the unwary. They may have referred to their previous function, the nation or tribe they were originally recruited from, an honorific they were give or just a nickname they acquired. So, the Lanciarii may have recruited from the old Legionary troops if that name, the Batavi may have been originally recruited from that tribe, the Undecimani may have earned that title for never been defeated or retreated from a battle and the Leones may have acquired that name either for being as fierce as lions or for having long hair.