About 1290 it first passed into the hands of Obizzo d'Este, and the authority of the Este family was after many vicissitudes more formally recognized in 1409.
Shortly afterwards he induced Alphonso d'Este, son of the duke of Ferrara, to marry her, thus establishing her as heiress to one of the most important principalities in Italy (January 1502).
The chart of the world by Juan de la Cosa, the companion of Columbus, is the earliest extant which depicts the discoveries in the new world (150o), Nicolaus de Canerio, a Genoese, and the map which Alberto Cantino caused to be drawn at Lisbon for Hercules d'Este of Ferrara (1502), illustrating in addition the recent discoveries of the Portuguese in the East.
At the beginning of the 11th century the citizens established a constitution, composed of a general council or legislative assembly and a credenza or executive; and during the next century they were engaged in wars with Venice and Vicenza for the right of water-way on the Bacchiglione and the Brenta - so that, on the one hand, the city grew in power and selfreliance, while, on the other, the great families of Camposampiero, D'Este and Da Romano began to emerge and to divide the Paduan district between them.
The citizens, in order to protect their liberties, were obliged to elect a podesta, and their choice fell first on one of the D'Este family (c. 1175).
Ferrara was then a gay and bustling town of 100,000 inhabitants, its prince Borso d'Este a most magnificent potentate.
In 1288 Obizzo d'Este was recognized as lord of the city; after the death of his successor, Azzo VIII.
Constituted a duchy in 1452 in favour of Borso d'Este, and enlarged and strengthened by Hercules II., it became the ducal residence on the incorporation of Ferrara with the States of the Church (1598).
On the motion, however, of Ippolito d'Este, the papal legate, exception was taken to the further conduct of the negotiations in full conclave; and a committee of twenty-four representatives, twelve from each party, was appointed - ostensibly to facilitate a satisfactory decision.