Martini painted a polyptych for the Sant'Agostino church. The work is nowadays dispersed over three different museums.
See fr.wikipedia.org

Martini was born in Siena. Several frescoes, among which his "Maestà", are in the Palazzo Pubblico.
See fr.wikipedia.org

"According to late Renaissance art biographer Giorgio Vasari, Simone was (...) a pupil of Giotto di Bondone, with whom he went to Rome to paint at the Old St. Peter's Basilica".
See en.wikipedia.org

Martini died in Avignon, while serving the Papal Court. Some of his works – detached frescoes and their sinopia – are visible at the Palais des Papes.
See en.wikipedia.org

The Romanesque church of Santi Stefano and Degna in Castiglione d'Orcia houses a 'Madonna with Child' by Simone Martini.
See en.wikipedia.org

The San Martino Chapel in the lower church of the Basilica of San Francesco d'Assisi features frescoes by Martini.
See en.wikipedia.org