What is "oltrarno"

The Oltrarno is a quarter of Florence, Italy. The name means beyond the Arno (compare to the Roman quarter of Trastevere); it is located south of the River Arno. It contains part of the historic centre of Florence and many notable sites such as the church Santo Spirito di Firenze, Palazzo Pitti, Belvedere, and Piazzale Michelangelo.