This thesis argues for the significance of castellated civic palaces in shaping and consolidating Florence’s territorial hegemony during the fifteenth century. Although fortress-like civic palaces were a predominant architectural type in Tuscan communes from the twelfth century onwards, it is an understudied field. In the literature of Italian Renaissance civic and military architecture, the castellated motifs of civic palaces have either been marginalised as an outdated and anti-classical form opposing Quattrocento all’antica taste, or have been oversimplified as a redundant object lacking defensive functionality. By analysing Michelozzo’s Palazzo Comunale in Montepulciano, a fifteenth-century castellated palace resembling Florence’s thirteenth-century Palazzo dei Priori, this thesis seeks to address the ways in which castellated forms substantially legitimised Florence’s political, military and cultural supremacy. Chapter One examines textual and pictorial representations of Florence’s castellation civic palaces and fortifications in order to capture Florentine perceptions of castellation. This investigation offers a conceptual framework, interpreting the profile of castellated civic palaces as an effective architectural affirmation of the contemporary idea of a powerful city-republic rather than being a symbol of despotism as it has been previously understood. Chapters Two and Three examine Montepulciano’s renovation project for the Palazzo Comunale within local and central administrative, socio-political, and military contexts during the first half of the fifteenth century, highlighting the Florentine features of Montepulciano’s town hall despite the town’s peripheral location within the Florentine dominion. Chapter Four casts light on the effective agency of Michelozzo’s castellated design in facilitating an architectural dialogue between civic and military, medieval and Renaissance, classical and modern, and centre and periphery, enhancing civic coherence in the town, as well as across the whole Florentine state. By looking at Michelozzo’s mid-fifteenth century design, this thesis demonstrates the interdependence of communal palaces’ castellated forms and their civic functions.