Leonardo marked Arezzo on maps RL 12278 and RL 12682 (Royal Collection, Windsor Castle) and mentioned the city on map RL 12277, in the Codex Atlanticus (f. 127r), and in the Codex Leicester (f. 9r). The city was a focal point in the hydro-engineering studies that he conducted beginning in 1495 or earlier for a project to divert the course of the Arno River.
Arezzo was one of the principal cities in Tuscany during Leonardo’s lifetime, a prosperous commercial centre from which highways departed toward the Adriatic. It attracted many artists, who embellished the city with such works as the Legend of the True Cross by Piero della Francesca, a masterpiece that Leonardo probably had occasion to admire and which can still be seen today in the Basilica di San Francesco. Arezzo was contested over during the stormy period of the condottiero Vitellozzo Vitelli and the fleeting rule of Cesare Borgia around 1502.
The Duomo of Arezzo is decorated with a series of the stained glass windows by the maestro vetraio Guillaume de Pierre de Marcillat (1475-1529) and I have recently suggested that one of the figures in the scene of the Resurrection of Lazarus, executed by him around 1520, could be Leonardo. Marcillat was a French artist who collaborated with Bramante and Raffaello, and the young Giorgio Vasari worked for a period in his atelier..