This article explores the connection between the castellated façade of Montepulciano’s Palazzo Comunale and Florence’s development into a territorial state in the mid-fifteenth century. In 1440, the comune of Montepulciano commissioned a new façade for its town hall from the prominent Florentine architect Michelozzo. While scholars have widely accepted Michelozzo’s design as an imitation of Florence’s Palazzo della Signoria, hitherto unpublished documents preserved in Montepulciano’s Biblioteca Comunale e Archivio Storico ’Piero Calamandrei’ enable further interpretation of the town hall’s fortress-like profile from a geopolitical and military perspective. According to the new textual evidence, Montepulciano maintained a close cooperation with the Dieci di Balìa — Florence’s war committee — from the late 1430s onwards and contributed to its military efforts against Milan, which climaxed in the battle of Anghiari the same year that the façade renovation was initiated. In view of Florence’s decisive victory in the battle, this article argues that the familiar castellated appearance of the new façade was a celebratory manifestation of the city’s military pride and that this was shared by the town. The architecture of the town hall can also be seen as testifying to the role played by castellation in expressing Florence’s territorial ideology.