Scutanann are heavy skirmishers, equipped with the famous scutum shield and a fair number of javelins. Unlike the lighter and more versatile Caetranann, whose primary tasks are raiding and flanking, the Scutanann are meant to hold a line, using their javelins to mow down enemy cavalry, whilst using their heavy scuta to fend off attacks by melee infantry . Their weight and lack of mobility however means that they are often at a disadvantage if they are used against light infantry or anti-personnel weapons such as the Scorpio, and as such ought to be used to form the first or second lines where they are not threatened by missile units. Additionally, as a pool of "semi-mercenary" units, Scutanann are not cheap as they must be recruited using Wealth.
If you are playing as the Celtiberians and are facing melee-heavy factions such as the Macedonians or Suebi, consider upgrading your Scutanann to Scutanann Loricati, or otherwise use your Skirmisher Levy or Caetranann units to hold off your enemy's missile units.In contrast to the Celtiberian style of play, the Lusitanians always have access to two different units of Scutanann: the aforesaid "vanilla" Scutanann, and the more powerful Arjos Scutanann ,