He was specially devoted to the Virgin Mary, and wrote an Officium Beatae Virginis, in addition to many letters, sermons, and other writings.
They are held in the public square, the curious and historic Piazza del Campo (now Piazza di Vittorio Emanuele) in shape resembling an ancient theatre, on the 2nd of July and the 16th of August of each year; they date from the middle ages and were instituted in commemoration of victories and in honour of the Virgin Mary (the old title of Siena, as shown by seals and medals, having been "Sena vetus civitas Virginis").
All that is certainly known about the antiquity of the sieu is that they were well established in the 3rd century B.C. Their initial point at the autumnal equinox marked by Kio (Spica Virginis) suits a still later date; and there is no valid evidence that the modern series resulted from the rectification of an older superannuated arrangement, analogous to the Krittika sequence of nakshatras.
The cathedral (Beatae Mariae Virginis) is one of the finest churches in Germany.
Sta Maria del Parto, in the Chiaja, occupies the site of the house of Sannazaro, and is named after his poem De Partu Virginis.