Solduros are disciplined elite soldiers, exhibiting great tenacity and proving themselves a sturdy force in any battle line.
The Solduros (Sul-dur-ohs; "Devoted Ones") are remarkably skilled, fearless elite guards of Celtic nobles. They pledge themselves to eachother and their charge, and fight to the very end. Small in number, they are a remarkable elite, best used to combat an enemy's opposing elite soldiers or heavy troops. They are very well armored and armed, and can surely break many enemies, but they are rare, very expensive, and while their armor and shields are of good quality, they have no form of retaliation at range, and would be too slow to chase off skirmishers or missile troops, and so would need ranged or cavalry support to be used to best effect.
Historically, Celtic nobles surrounded themselves with elite bodyguards of kings, magistrates, and other important nobles and officials, such as high ranking druids. Among them were the "Soldurii", the greatest warriors of the Aquitanni. Each man pledged his life to a fellow of this brotherhood, and the man pledged to would return this pledge; if the one of these two died, and the other did not, the remaining man would take his own life after the battle, for having failed defend him. Julius Caesar noted that no man ever backed down from this duty, and did so fearlessly. Their skill was tremendous; they fought against great odds and could defeat many times their own number. So great and legendary was their name even to their enemies that it can be found having influenced words such as 'soldier' and 'solidarity'.
The "standard" elite force of Gallic factions, Solduros are very reliable and hard to beat. They are effective against both infantry and cavalry, and can stand up to the best troops the enemy can muster. As a typical elite infantry unit, they can be used as the core of your battle line, but also as assault troops, flankers, or elite reserve. Because of their heavy armour and large shields, Solduros can shrug off most missiles coming from the front, which is all the more important since they are one of the very few Celtic units that are capable of resisting missile fire to such a degree.
Take care though that they don't get swamped by hordes of enemy axemen or falxmen - in multiplayer games, a good opponent is aware of the strengths and weaknesses of your units and will try to counter them.