The Latin language has been the one constant in the cultural history of the West for more than two millennia. It has defined the way in which we express our thoughts, our faith, and our knowledge of how the world functions, its use echoing on in the law codes of half the world, in the terminologies of modern science, and, until forty years ago, in the liturgy of the Catholic Church. In his erudite and entertaining “biography,” Nicholas Ostler shows how and why Latin survived and thrived even as its creators and other languages failed.