The Serchio is the third longest river in the Italian region of Tuscany at 126 kilometres, coming after the Arno at 242 kilometres and the Ombrone, 161 kilometres. By mean rate of flow, it is the second largest, smaller than Arno but larger than Ombrone.
The principal source forms on the slopes of Monte Sillano, elevation 1,864 metres and is joined by a secondary branch, the Serchio di Gramolazzo, at Piazza al Serchio.
