http://en.wikipedia.org/wiki/Religion
Religion is derived from the Latin religiō, the ultimate origins of which are obscure. One possibility is derivation from a reduplicated *le-ligare, an interpretation traced to Cicero connecting lego "read", i.e. re (again) + lego in the sense of "choose", "go over again" or "consider carefully". Modern scholars such as Tom Harpur and Joseph Campbell favor the derivation from ligare "bind, connect", probably from a prefixed re-ligare, i.e. re (again) + ligare or "to reconnect," which was made prominent by St. Augustine, following the interpretation of Lactantius. However, the French scholar Daniel Dubuisson notes that relying on this etymology "tends to minimize or cancel out the role of history"; he notes that Augustine gave a lengthy definition of religio that sets it quite apart from the modern word "religion".
^... What is called ancient religion today, they would have only called "law".