Pietro Lorenzetti (Siena, Italy, c. 1280 – Siena, Italy, 1348) was an Italian Byzantine Style painter of the Sienese school. He and his brother Ambrogio were precursors of the art of the Renaissance. Lorenzetti worked in Siena, Arezzo, Assisi, Florence, Pistoia, and Cortona. He had the influence of Duccio di Buoninsegna, of the Sienese School, Giotto di Bondone and Giovanni Pisano.
Many of his religious frescoes are in churches in Siena, Arezzo, and Assisi. His masterworks are in the Basilica of San Francesco d'Assisi (i.e. Crucifixion, Deposition of Christ from the Cross, Last Supper, and Stigmata of St. Francis). Other main works include The Madonna and Child with St. Francis and St. John the Evangelist, The Carmelite Altarpiece, Madonna with Angels between St. Nicholas and Prophet Elijah, the Uffizi Madonna, and the triptych altarpiece, Birth of the Virgin, commissioned for the Siena Cathedral.
It was only toward the end of his career that Pietro developed his considerable narrative powers, which were delicately and tenderly expressed in one of his masterpieces, a triptych dedicated to the Nativity of the Virgin. 
Fresco "Triumphal Entry into Jerusalem", Lower Basilica, San Francesco, Assisi, Italy, 1320.