A book is rounded to help prevent the spine from falling in, i.e., assuming a concave shape (and a convex fore edge), which would result in severe strain on the hinges of the book. It also facilitates the outer sections being knocked over to form the backing shoulders, and, in conjunction with this backing process, helps accommodate the swell in the spine resulting from the bulk added by the sewing threads.
The practice of rounding the spines of books dates back to at least the middle of the 15th century, and, during the course of years, the "proper" shape of the round has ranged from a nearly flat spine to a highly exaggerated arc. See a/so: BACKING ;ROUND BACK . (161 , 196 ,236 , 335 )
Timestamp: Saturday, 19-Nov-2011 13:18:44 PST
Retrieved: Wednesday, 20-Feb-2019 07:26:31 GMT