[Child-of-the-Emperor]

They were all originally 10,000 at the beginning of the Great Crusade :victory:

Its been said before, but i'll say it again - there are no definitive Legion sizes because different authors and different fans take differing stances.

I read somewhere that the Ultramarines had 250,000 just before the Horus Heresy. That was the largest legion due to their success on the eastern fringe.

The Collected Visions claims that the Ultramarines maintained a Legion size of 250,000. But it also claims that the average Legion size was ~100,000. Most of the Heresy series seems to think differently. As I said though, the Legion sizes depend on the author.

While one of the legions, can't remember which was at one point only 200 marines due to an accident/ massive tactical error? :headbutt:

That would be the Emperor's Children.