Bordering one side of Piazza San Francesco is the austere exterior of the massive Basilica of San Francesco, an exterior which reflects the austerity of Franciscan life. This austerity is, however, tempered with the beautiful rose window that breaks up the facade and the slender elegance of a bell tower.
Like the troubled Hosts within, the Basilica's exterior has also undergone periods of turbulence. A church was first constructed on the site in the early 12th-century but the decision was made to rebuild it a century later. A fire almost certainly destroyed this church in 1655 while in the late 19th-century another replacement was created in the Purist style of Giuseppe Partini. Paolo Posi designed the fine lines of the bell tower, added in 1765. For the last century or so, the Basilica has enjoyed a well-earned period of peace.
The Basilica's interior reflects the more ornate cathedral but overall, it is simpler and less decorative in style. Of particular note among the frescoes by Ambrogio Lorenzetti is the Martyrdom of Five Franciscan Friars by Pope Boniface VIII and the Madonna del Latte.
What draws visitors and pilgrims to the Basilica, however, is not its art but an event that took place in 1730 when sacrilegious thieves stole a silver pyx holding 351 consecrated Hosts or communion wafers. So momentous was this theft, that even the annual Palio was canceled. The Hosts were discovered after three days and brought back to Siena in a solemn procession. Regular checks on them since their return show that they have remained miraculously whole and fresh. Churches across Siena still hold masses in homage to this remarkable event.
For the last century, the Basilica has had a more peaceful existence and welcomes visitors who come to admire its frescoes and art collection from the Sienese school. These include the Coronation of the Virgin by Sassetta and Sano di Pietro, the Crucifixion by Pietro Lorenzetti, the Nativity of Christ by Sodoma, and two frescoes by Ambrogio Lorenzetti. At the end of the right-hand transept is a 14th-century statue of Saint Francis while a chapel to the right of the choir contains the tomb of Cristoforo Felici worked by Urbano da Cortona in 1462.
Within the imposing might of the Basilica of San Francesco are two cloisters which take visitors back to the early history of the first church and monastery.
Franciscan monks first arrived in Siena in 1226 after the death of Saint Francis of Assisi. They erected their monastery on the present site. The Franciscan order followed a rule of austerity both in architecture and conduct, aspects reflected in the present outline of the building.
When visitors step through a door near the Chapel of the Sacrament they enter the delicate proportions of the spacious Renaissance Cloister. Within the Cloister are some sculpture fragments from the early 14th-century which are believed to be by Domenico d'Agostino. The Franciscan convent building still stands next to the church, but today is home to the University of Siena's Law Faculty and Department Library.