Board Thread:Naruto Discussions/@comment-25139119-20140905185119/@comment-25389387-20140905212755

From what i've read on the wikia and such, the Ten-Tails was initially sealed inside of Hagoromo. It was later during the waning days of the Sages life when he (and probably his brother) realized that when he died the Ten-Tails would be unsealed and create the same destruction as before. When that was realized the Ten-Tails chakra was removed and split into the current 9 Tailed Beasts. Its body was also sealed into the Chibaku Tensei afterwards.

Again, this is what I've gotten from reading various pages on the wikia. Hope this might help a bit.