The feast day of Saint Isidore of Seville is celebrated on April 4th in the Roman Catholic Church. Saint Isidore of Seville was a bishop and theologian who lived in Spain during the sixth and seventh centuries. He is known for his prolific writings and for his contributions to the development of Christian theology, education, and liturgy. He was a renowned scholar, and his most famous work, the Etymologiae, was a popular encyclopedia of its time. Saint Isidore was venerated as a saint in the Catholic Church in the ninth century, and his feast day is celebrated by Catholics around the world.