From Wikipedia on anal sex
Anal sex is thought to have been so common in Ancient Greece that the term "Greek love" was used to refer to the practice, and in modern times, "Doing it the Greek way" is sometimes used as slang for anal sex. However, the view that homosexual anal sex was a commonly accepted practice in Ancient Greece is widely debated. Pederasty was an important part of society in Ancient Greece, as the bond between a young man and an older man was seen to help in his maturation. These relationships often included sex but not always. There are certainly many works of pottery and other art that display anal sex between older men and boys, as well as some depicting only adult men. Some literature has argued that the important social transgression was lowering oneself socially, that is, a high status person was not supposed to be penetrated by a lower status person, and thus passive anal intercourse by such men would have been frowned upon and considered a serious moral transgression. Much evidence exists that shows great tolerance for homosexual relationships, but it was generally expected that these relationships would not preclude heterosexual relationships, due to the need for procreation. How acceptable anal sex was may have varied depending on the time-period, as Ancient Greece spanned a long time. Male passive anal intercourse was (traditionally) frowned-upon in Rome, while playing the active role with a slave was acceptable. In fact the Romans thought of anal sex as something particularly "Greek". Others have argued that in Greece, rather than anal sex, male-male couples actually engaged in non-penetrative interfemoral intercourse. However, this view has been disputed. The historian K.J. Dover discusses these matters thoroughly in his classic work Greek Homosexuality. Also disputed is the assertion that Greek courtesans, or hetaerae, frequently practiced heterosexual anal intercourse as a means of preventing pregnancy.