Despite the difficulties, John issued a new statute of Vilnius
cathedral chapter in 1520, called the first known
diocesan synod in 1520 or 1521, and, with pope's permission, created two new
prelates of the cathedral chapter (in charge of
scholastics and
choir) in 1522. John also received papal legate
Zacharias Ferrerius sent to investigate canonization of
Saint Casimir after a miracle attributed to him during the
Siege of Polotsk (1518). John paid attention to education. In 1522, he revised the curriculum of the
Cathedral School of Vilnius to include
rhetoric,
dialectics, classical literature, arithmetic, music. In 1526 or 1527, John called the second diocesan synod which debated three major topics: improper behavior by priests, proper procedures of church services, and establishment of schools. The results of the proceedings were published in Kraków in 1528. The synod decided that each parish church should have a school that would instruct children in both Polish and Lithuanian languages. The synod also forbade hiring German teachers or traveling priests as they could be influenced by
Lutheranism. His father Sigismund I the Old gifted John with
Šiauliai in 1524,
Zhytomyr in 1525, and
Kremenets in 1529. That was enough to make him a very wealthy
magnate – the
military census of 1528 placed him the ninth wealthiest. He funded repairs and reconstruction of
Vilnius Cathedral and its belfry (architect Adam Annus). In June 1530, a large fire devastated Vilnius Cathedral. The repairs were slow and Italian architects
Bernardino de Gianotis and Giovanni Cini were hired only in July 1534. John sponsored construction of a new church in Šiauliai in 1526. He established new parishes and built churches in
Joniškis (named so after himself),
Gervyaty, and
Zarasai. In total, during his tenure as Bishop of Vilnius, more than 30 new churches were built in the diocese. On 18 October 1529, John crowned his half-brother
Sigismund II Augustus as Grand Duke of Lithuania. In June 1535, John was appointed overseer of
Vilnius Mint when it temporarily reopened during the
Muscovite–Lithuanian War. In March 1536, Queen
Bona Sforza, who disliked John, managed to get John removed from Vilnius to the
Diocese of Poznań. He died there just two years later but, according to his last will, he was buried in Vilnius Cathedral. A new chapel, known as the Chapel of Bishops or Chapel of the Holy Sacrament, was built according to his last will around 1548. His tomb monument of
Pińczów limestone was ordered by his brother Sigismund Augustus in 1556. It was designed by
Giovanni Maria Mosca also known as Padovano, but did not survive. ==References==