Edit: Or not. Either it was a glitch on Springer’s part, or an extremely short term offer. The books no longer appear to be free. It was nice while it lasted.
Springer has made a big chunk of its catalog of archaeology and other scientific and technical books freely available for download. There are almost 400 archaeology and anthropology books available, including Dent’s Chesapeake Prehistory, Odell’s Lithic Analysis, most/all volumes of the Encyclopedia of Prehistory, and many more. Titles include underwater archaeology, geoarchaeology, historical archaeology, and biological anthropology. See the books at Springer.