Leander, Isidore, and their siblings belonged to an elite family of Hispano-Roman stock of Carthago Nova. Leander was born in 534. Their father Severianus was a governor of Cartagena The family were devout Catholics, as were most of the population. The Visigothic nobles and the kings were Arians.
The family moved to Seville around 554. Leander and Isidore, his brother both became bishops of Seville, and their sister Saint Florentina was an abbess who directed forty convents and one thousand nuns. The third brother, Fulgentius, was appointed Bishop of Écija. All four siblings are considered saints of the Roman Catholic Church.
There was Visigothic persecution of Catholics, though most dangers of Catholicism were political. The Catholic leaders were supportive of the Byzantine emperor, who had territory south of Hispani.
Leander had an elite position of a tolerated Catholic culture in Seville. He became a Benedictine monk in 576 and in 579 he was appointed bishop of Seville. He founded a school, which soon became a center of Catholic learning. As bishop, he had access to the Catholic Merovingian princess Ingunthis, who was a bride for the kingdom’s prince. He helped her to convert her husband Hermenegild, the eldest son of Liuvigild. Leander defended the prince when he went to war with his father against Arianism. Leander was a devout Christian and a patriot.
Leander was exiled by Liuvigild from 579 to 582. While in exile he wrote against Arianism and there became acquainted with the future Pope Gregory the Great. They formed a close friendship. In 585 Liuvigild put his son, Hermenegild, the prince to death. He is a martyr and saint of the Catholic Church. Liuvigild died in 589. It is not known exactly when Leander returned from exile.
Leander introduced the recitation of the Nicene Creed at Mass, as a way to help reinforce the faith of his people against Arianism. In 589, he called for the Third Council of Toledo, to continue fighting Arianism. He and his brother Saint Isidore never stopped fighting Arianism. Leander died on March 13, 601.