The first Roman emperor to have married a man was Nero, who is reported to have married two other males on different occasions. The first was with one of Nero's own freedmen, Pythagoras, with whom Nero took the role of the bride.[107] Later, as a groom, Nero married Sporus, a young boy, to replace the adolescent female concubine he had killed[108][109] and married him in a very public ceremony with all the solemnities of matrimony, after which Sporus was forced to pretend to be the female concubine that Nero had killed and act as though they were really married.[108] A friend gave the "bride" away as required by law. The marriage was celebrated in both Greece and Rome in extravagant public ceremonies.[110]
Conubium existed only between a civis Romanus and a civis Romana (that is, between a male Roman citizen and a female Roman citizen), so that a marriage between two Roman males (or with a slave)
would have no legal standing in Roman law (apart, presumably, from the arbitrary will of the emperor in the two aforementioned cases).[111] Furthermore, according to Susan Treggiari, "matrimonium was then an institution involving a mother, mater. The idea implicit in the word is that a man took a woman in marriage, in matrimonium ducere, so that he might have children by her."[112]
Same-sex marriage - Wikipedia