The first historical mention of the performance of same-sex marriages occurred during the early Roman Empire according to controversial historian John Boswell. These were usually reported in a critical or satirical manner. Child emperor Elagabalus referred to his chariot driver, a blond slave from Caria named Hierocles, as his husband. He also married an athlete named Zoticus in a lavish public ceremony in Rome amidst the rejoicings of the citizens.
The first Roman emperor to have married a man was Nero, who is reported to have married two other males on different occasions. His first marriage was with one of his freedmen, Pythagoras, with whom Nero took the role of the bride. Later, as a groom, Nero married Sporus, a young boy, to replace the teenage female concubine he had killed  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. A friend gave the "bride" away as required by law. The marriage was celebrated in both Greece and Rome in extravagant public ceremonies.
It should be noted, however, that 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). 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." Still, the lack of legal validity notwithstanding, there is a consensus among modern historians that same-sex relationships existed in ancient Rome, but the frequency and nature of "same-sex unions" during that period are obscure.
In 342 AD Christian emperors Constantius II and Constans issued a law in the Theodosian Code (C. Th. 9.7.3) prohibiting same-sex marriage in Rome and ordering execution for those so married.
A same-sex marriage between the two men Pedro Díaz and Muño Vandilaz in the Galician municipality of Rairiz de Veiga in Spain occurred on 16 April 1061. They were married by a priest at a small chapel. The historic documents about the church wedding were found at Monastery of San Salvador de Celanova.