Battle of Montaperti The Battle of Montaperti was fought on September 4 , 1260 , between Florence and Siena in Tuscany as part of the conflict between the Guelphs and Ghibellines . It gained notoriety for an act of treachery that turned the tide of the battle , which was immortalised by Dante Alighieri in his epic poem " Divine Comedy " . Prelude . The Guelphs and Ghibellines were rival factions that nominally took the parts of the Papacy and the Holy Roman Empire , respectively , in Italy in the 12th and 13th centuries ; in practice , their allegiances often had more to do with competing local interests than with the contesting claims of the papacy and the Empire . In the mid - 13th century , Guelphs held sway in Florence whilst Ghibellines controlled Siena . In 1258 , the Guelphs succeeded in expelling from Florence the last of the Ghibellines with any real power ; they followed this with the murder of Tesauro Beccharia , Abbot of Vallombrosa , who was accused of plotting the return of the Ghibellines . The feud came to a head two years later when the Florentines , aided by their Tuscan allies ( Bologna , Prato , Lucca , Orvieto , San Gimignano , San Miniato , Volterra and Colle Val d ' Elsa ) , moved an army of some 35 , 000 men toward Siena . The Sienese called for help from King Manfred of Sicily , who provided a contingent of German mercenary heavy cavalry . The Sienese forces were led by Farinata degli Uberti , an exiled Florentine Ghibelline . Even with these reinforcements , though , they could raise an army of only 20 , 000 . Battle . The two armies met at the hill of Montaperti , outside Siena , on the morning of September 4 ; at the head of the Sienese army was the formidable band of German mercenary cavalry . The battle raged all day , but despite their superior numbers , the Florentines were unable to make headway against the determined Sienese . As evening approached and the Florentines exhausted themselves on their opponent ' s defensive lines , the Sienese forces launched their counterattack , led by the Count of Arras . The charge of the Sienese was a signal to a member of the Florentine forces , Bocca degli Abati . Bocca had been a partisan of the Guelph for the sake of complex allegiances , but was at heart a Ghibelline . At the sign of the counterattack Bocca made his way across the Florentine lines toward the standard - bearer of the Florentines and hacked off the hand that held the standard , causing the Florentine colors to fall . As land battles were waged at that time , the standard was vital ; it showed that one ' s forces were intact and fully engaged . The fall of the standard caused provoked confusion among the Florentines . Seizing the opportunity , hundreds of Florentine Ghibellines attacked their Guelph compatriots as the main Sienese army charged , and the Florentine Guelphs were routed , pursued by their enemies as they fled . It is estimated that 10 , 000 men died on the Guelph side . After the battle , the German soldiers in the Sienese army used part of their pay to found the Church of San Giorgio in Pantaneto — the Germans had called on Saint George as their battle - cry during the battle . Depiction in the " Divine Comedy " . Dante studied under Florence ' s Chancellor Brunetto Latini , who was himself away from the battle scene , on embassy in Castile seeking help for Guelph Florence from Alfonso X el Sabio . Dante would have learned of the battle , its preparations ( documented by Latini in the " Libro di Montaperti " ) , strategies and treachery , as well as those of the Battles of Benevento and Tagliacozzo , from the Chancellor , using material also to be gleaned later by Giovanni Villani , the Florentine merchant and historian . As a result Dante reserved a place in the ninth circle of Hell for the traitor Bocca degli Abati in his " Divine Comedy " : The Ghibelline commander Farinata degli Uberti is also consigned to Dante ' s hell , not for his conduct in the battle , but for his alleged heretical adherence to the philosophy of Epicurus .