They appear to be powered by some sort of combustion, releasing smoke and sometimes exploding when defeated. Not all Anchor are identical; their designs appear to vary based upon their craftsperson or some other variable.
The Anchor cannot act independently, but must follow orders from someone with authority. Ordennan officers may possess a small steel tag that allows them to control the Anchor for a given purpose. Use of the tag requires a 'sacrifice' that inflicts pain upon the user; doing so, Hella was able to take possession of such a tag and turn the Anchor back onto the Ordennnans. With difficulty, Hadrian was able to use the strength of Samothes to control a single soldier without possession of such a tag.