The heated historical rivalry between Bologna and Modena was born from a desire for conquests and opposite political positions: Guelphs (Bologna), allies of the pope and Ghibellines (Modena), allies of the emperor. Fight for investitures and border war mingled and led to tragic events.
In Modena after the death of Orbizzo d'Este, a struggle for succession had started. Among the children, Azzo VIII prevailed, who launched the gauntlet in Bologna, in an attempt to strengthen his prestige and have the support of the nobility. This episode intensified the spirits and the war along the border became even more violent, a war from which the Modenese nobleman came out defeated. Upon his death, his successor continued and tightened the tension between the two cities.
In 1296 the Bolognese had invaded the lands of Bazzano and Savignano, effectively removing them from the Modenese, thanks also to the support of Pope Boniface VIII who officially recognized the Guelph possession of the castles of the aforementioned localities.
The Pope thus intended to strengthen his power over the Bolognese, who saw in the Ghibellines of Modena, the main enemy for the ancient question of borders.
Bologna had in fact enlarged its territorial aims, having to face the demographic increase consequent to the fame of its university.
Conquests, reconquests and looting followed until the Modenese forces conquered the castle of Monteveglio, which constituted an important bulwark for the defense of Bologna. Zappolino and its castle then became the last important stronghold in defense of today's Emilian capital. The battle that took place at the foot of the Zappolino hill, on November 15, 1325 towards the setting of the sun just outside the castle walls, represented one of the biggest clashes that took place in the Middle Ages. In fact, about 35,000 infantrymen and 4,000 knights and more than two thousand men lost their lives on the battlefield.The Bolognese did not have much time available to organize the troops, having hastily recalled them from other conflict areas where the modenesi they had attracted with some stratagems and by advancing towards Monteveglio for the reconquest of his castle. The battle was short and intense and ended with the terrible defeat of the Bolognese army. Despite the numerical superiority, the Bolognese troops, taken by surprise by a lateral attack, dispersed. Many men took shelter in the castle of Zappolino, others in that of Oliveto, others still followed, chased, Bologna, finding refuge among its walls. The people of Modena came to the gates of the city (destroying the castles of Crespellano, Zola, Samoggia, Anzola, Castelfranco, Piumazzo and the Reno lock at Casalecchio as they passed, which allowed, as today, the diversion of the river waters towards the city) but they never entered, limiting themselves to remain outside its walls and finally return to Modena carrying a bucket stolen in a well as a trophy (well still existing under a manhole outside S. Felice gate in Bologna).
A few months later, in January 1326, the peace signed by the two sides saw the return of the lands and castles conquered by the Ghibellines to the Bolognese.
Inspired by the episode of the well, in the 1600s, Alessandro Tassoni wrote a heroicomic poem entitled "La secchia rapita". Where, the refusal of the people of Modena to return the bucket, a heated war breaks out for its reconquest. Various imaginary characters and even the Olympians also participate in it, distributed between the two parties.
The war for the kidnapped bucket lasts for some time between battles, duels, truces and tournaments, interspersed with comic and burlesque episodes that often have the Count of Culagna as protagonist who at the end of the conflict concludes stating that the Bolognese can be held prisoner king Enzo but the people of Modena keep the bucket.
During the conflict, King Enzo, son of Emperor Frederick II, also fought in favor of the people of Modena. That following the defeat of the battle of Fossalta, in May 1249, he was captured by the Bolognese at the gates of Modena. First locked up in the castles of Castelfranco and Anzola dell'Emilia, he was then taken to Bologna and imprisoned in the new town hall adjacent to Piazza Maggiore, which was later called Palazzo Re Enzo for this. Most of the prisoners could obtain freedom after paying a ransom but despite the insistence and offerings of the emperor the Bolognese always refused to surrender the prisoner and Enzo was imprisoned for life; although with a fairly comfortable treatment, he could in fact rejoice with poetry and literature as well as with the company of ladies (from whom he also had children). After twenty-three years of captivity, and an attempt to escape to a "brenta", he died in Bologna on March 14, 1272 and was buried at the basilica of San Domenico with splendid honors at the expense of the municipality of Bologna.