Infant mortality -ancient world

[Epictetus]

You might try Brunt's Italian Manpower. Unfortunately I read a library copy, so don't have it handy to cite anything, but I do remember he claimed that almost the entire growth of the city of Rome itself came from immigration because the mortality rate was so high in the urban area. It was a fascinating book. Brunt also freely admitted what we don't know about the ancient population, which is quite a lot. The book was published in the 1970s, I think, so there are probably more recent estimates out there now.

Doing some internet searching of scholarly journals, I found numbers ranging from 25% to 40%.