The Elsa valley is one of the most beautiful parts of Tuscany. Once a crucial part of the "Via Francigena" (The Frankish Route) that linked Rome to Northern Europe by pilgrimage and trade, the valley's fortunes rose in the 8th century, when the Lombards (think Charlemagne) realised that the Elsa valley is protected by a range of hills from the mediterranean coast, which at that time was still controlled by the Byzantine navy operating from Constantinople.
Because of this protection the valley became a thoroughfare of trade and pilgrimage that made the fortunes of cities like Siena, and many of the other smaller towns on this route.
