When Carlo arrived they decided to lose no more time, and assembled a great army of more than thirty thousand infantry and ten thousand cavalry--having called to their aid every Guelph there was in Italy.

They consulted whether they should attack Pistoia or Pisa first, and decided that it would be better to march on the latter--a course, owing to the recent conspiracy, more likely to succeed, and of more advantage to them, because they believed that the surrender of Pistoia would follow the acquisition of Pisa.
In the early part of May 1328, the Florentines put in motion this army and quickly occupied Lastra, Signa, Montelupo, and Empoli, passing from thence on to San Miniato.

When Castruccio heard of the enormous army which the Florentines were sending against him, he was in no degree alarmed, believing that the time had now arrived when Fortune would deliver the empire of Tuscany into his hands, for he had no reason to think that his enemy would make a better fight, or had better prospects of success, than at Pisa or Serravalle.

He assembled twenty thousand foot soldiers and four thousand horsemen, and with this army went to Fucecchio, whilst he sent Pagolo Guinigi to Pisa with five thousand infantry.

Fucecchio has a stronger position than any other town in the Pisan district, owing to its situation between the rivers Arno and Gusciana and its slight elevation above the surrounding plain.