Complex sentence: They arrived in Florence towards the end of the 12th century, coming from the areas of Poggibonsi and from the "Pesa" valley, which are between Siena and Florence.
Split into simpler sentences: They arrived in Florence towards the end of the 12th century. They came from the areas of Poggibonsi and from the "Pesa" valley, which are between Siena and Florence.