The church of St Mary became the city's cathedral in the 13th century. Few traces of the medieval structure remain: the steeple, the two Romanesque side doors and the so-called Pisan Chapel, dedicated to the Sacred Heart. As it is today, the cathedral has a latin-cross plan, with a transept and three naves. During the 17th century, the building underwent its first major reconstruction work. The inside and the façade were changed, following the Baroque fashion of the time. It was not until the 1930s that the façade was yet again restyled, according to a Neo-Romanesque pattern. The Sanctuary of the Martyrs hosted in the crypt is home to 179 niches containing relics of Cagliari's martyrs.