Intercourse by insertion of the
penis between the
thighs of the
partner rather than penetration of
vagina or
anus. This was a
common practice in
homoerotic relations between older and younger
men in
ancient Athens since
anal penetration was considered violating bodily
integrity and humiliating for the receiving end
(usually the younger man).
Needless to say, this method greatly reduces the risk of unwanted
pregnancy and sexually transmitted diseases. It can get rather
messy, though.