Having fixed upon a plan to be followed, Castruccio cautiously fortified the tower of the Onesti, filling it with supplies and munitions of war, in order that it might stand a siege for a few days in case of need.

When the night came which had been agreed upon with Uguccione, who had occupied the plain between the mountains and Pisa with many men, the signal was given, and without being observed Uguccione approached the gate of San Piero and set fire to the portcullis.

Castruccio raised a great uproar within the city, calling the people to arms and forcing open the gate from his side.

Uguccione entered with his men, poured through the town, and killed Messer Giorgio with all his family and many of his friends and supporters.

The governor was driven out, and the government reformed according to the wishes of Uguccione, to the detriment of the city, because it was found that more than one hundred families were exiled at that time.