The 'schiltron' (the Scottish term was schiltrum) is an immobile formation for barbarian spearmen. Every stands in a circle, every spearpoint outwards to fend off cavalry attacks and as a result it has no flanks for enemy horsemen to exploit. This is good.

The bad bit is that a unit in a schiltron is immobile, so it's a kind of passive-aggressive manouevre that can really cause problems if you don't have missile troops to counter it.

We did use the term 'hedgehog' for this formation for quite a long time and considered having this as the 'official' in-game term for it, because the word is a very good description of what the unit is doing. On the other hand, given that CA's new owners are Sega, putting a hedgehog in the game might have sent the wrong signals, realism-wise.