Incest of unequal gravity: the "incestus iuris gentium," which was applied to both Romans and non-Romans in the Empire, and the "incestus iuris civilis," which concerned only Roman citizens. Therefore, for example, an Egyptian could marry an aunt, but a Roman could not. Despite the act of incest being unacceptable within the Roman Empire, Roman Emperor Caligula is rumored to have had sexual relationships with all three of his sisters (Julia Livilla, Drusilla, and Agrippina the Younger). Emperor Claudius, after executing his previous wife, married his brother's daughter Agrippina the Younger, and changed the law to allow an otherwise illegal union.
Matthias, Holy Roman Emperor Matthias, Holy Roman Emperor Matthias (24 February 1557 – 20 March 1619) was Holy Roman Emperor from 1612, King of Hungary and Croatia from 1608 (as Matthias II) and King of Bohemia from 1611. He was a member of the House of Habsburg. Matthias was born in the Austrian capital of Vienna to Maximilian II, Holy Roman Emperor and Maria of Spain. Matthias married Archduchess Anna of Austria, daughter of his uncle Archduke Ferdinand II of Austria, whose successor in Further Austria Matthias became in 1595. Their marriage did not produce surviving children. In 1578, Matthias was invited to the