St Catherine of Siena brought this basilica to prominence by taking her vows here in 1363 when she was just 15. Having had her first vision at the age of 6 near this church and deciding to follow a religious life from 7, she went on to lead a highly significant existence tending the sick, receiving the stigmata from a wooden cross in Pisa, mediating for the Papacy during its exile in France and also the time of Great Schism of the West when the cardinals could not agree on who should be the next pope. After dying at the age of 33 in Rome, St Catherine was made a saint in 1461 and then a patron saint before being proclaimed a co-patron saint of Europe in 1999.
Apart from having her spiritual origins in this church in Siena, St Catherine of Siena remains present in the church in the form of relics. Although buried in Rome, her head was returned to Siena where it is preserved above the altar of Basilica di San Domenico. In addition, her thumb and the whip she used for self-flagellation on behalf of the faithful are contained in a small window box to the right of the Chapel of Saint Catherine inside the basilica.