Board Thread:Lore Discussion/@comment-6702118-20140722142914/@comment-5989209-20140723044421

Alduin used to be large enough to consume all of Mundas and Oblivion, but he slacked off on his duties. However, the body seen in game is not mortal, no Dragon has a mortal body, and is nigh invunerable except when under the effects of Dragonrend. Even then, he's implied to be much larger than the way he is actually seen in game. Most people notice Alduin to be much larger than the average Dragon, for instance.