The circular church of Santa Costanza, also of the 4th century, served as a baptistery and contained the tomb of the daughter of Constantine.
After the death of Tancred the emperor Henry VI., of the house of Hohenstaufen, who by his marriage with Constance or Costanza d'Altavilla, daughter of Roger I.
Costanza then had her son Frederick (b.
Costanza died in 1198, leaving Pope Innocent III.
Regent and tutor to her son; the pope's authority was contested by various nobles, but in 1209 Frederick married Costanza, daughter of the king of Aragon, with whose help he succeeded in reducing a large part of Sicily to obedience.
He now became head of the Ghibellines or Imperialists of Italy, and his position was strengthened by the marriage of his daughter Costanza to Peter, son of King James of Aragon.