Once we passed Porta Romana, following the sign “Francigena sud”, we start biking in the countryside, along a track reaching the Grancia di Cuna and going back through a different path, going up the hills of Siena.
Entering the Strada di Certosa, we find the Certosa di Maggiano along a path far from the heavy traffic, going towards the Val d’Arbia in a variation of agile climbs and easy slopes.
The road is umpaved for a short stretch and approaching a little fountain becomes a cycle pedestrian path for a few hundreds’ meters. Through a short stretch of Francigena we reach Isola d’Arbia and biking in a suggestive macadam path that licks the inner city of Ponte a Tressa to the Grancia di Cuna, the southernmost point of the itinerary. Just after the railway underpass, we turn left in a dirt road leading to More di Cuna, passing along the public garden, we turn right towards the inner city entering the SS Cassia Road and we turn left in direction to Siena.
Before arriving in Ponte a Tressa, taking the short cycle pedestrian path next to SS2 Cassia, a very singular building does not go unnoticed. This is the former Idit of Isola d’Arbia, an industrial factory inaugurated in 1960 and operative for some years. Having reached Ponte a Tressa we continue through the Cassia up to km 219 and turn right along the Strada Comunale di Fonte Murata up to the Renaccio area. Here we find the signs to Florence-Siena- Grosseto, starting biking uphill for two kilometers. This is a not so demanding slope to reach again the road to Porta Romana.