Once in Modena, the Estes did not let these questions lapse; but for the whole of the 17th century the battle was fought exclusively on paper, with much written and verbal skirmishing between the Este court and the Roman Curia and, less directly, through a rather naive diplomatic campaign that often bordered on wishful thinking.
There is no doubt that one of duke Francesco I's objectives was to pave the way for a return to Ferrara and Comacchio. And, since his programme was known more or less everywhere, Italian and European diplomats were well aware that, in order to remain on friendly terms with the Estes, it was necessary to tackle this dispute.
When the so-called War of Castro broke out, the duke had tried to reconcile the differences between Odoardo Farnese and the Barberinis, but when this failed he fought tenaciously for the creation of the league of Venice, Tuscany, and Modena.
The league had been conceived to ensure peace in Italy, but very soon became a part of the coalition set up by the Farnese family against pope Urban VIII. But in reality the allies preferred to have the Papal State for a neighbour rather than a dukedom like that of the Estes, ruled by its restless and aggressive Lord.
The documents published at the time containing details of the Este case, the replies made by the Roman Curia, and the duke's prompt counter replies, obviously had no effect whatsoever; just as, on the occasion of the signing of the peace treaty in Ferrara, on 31 March 1644, the secret intelligence offered to Francesco - in which it was said that France and the League were prepared to look favourably upon his claims to the territories left in the hands of the Church by Cesare d'Este - emerged as purely formal, if not derisory.
Clumsily, Francesco had passed from an agreement with Spain to another with France, but the outcome of the war went against him, obliging him to accept the peace of 27 February 1649. During the ensuing talks in Madrid, the Este ambassador, count Francesco Ottonelli, once more brought up Este aspirations regarding Ferrara and Comacchio, but all in vain, a fact largely due to the Spaniards' understandable diffidence with regard to a duke who had cheerfully betrayed them only one year before.
At the beginning of the 18th century, political and dynastic objectives were to come together against a backdrop of events that concerned Italy and Europe as a whole. In 1695, Duke Rinaldo married the Princess Carlotta Felicita, the daughter of John Frederick, Duke of Brunswick and Lüneburg, and the niece of Ernest August, the Elector of Hanover, thereby reuniting, after over six centuries, the two ancient branches of the house of Este descending from the line of Alberto Azzo II.
Between 1702 and 1707, the War of the Spanish Succession had led to the occupation of Modena by French troops, followed by the Austrians in 1708. Under duke Rinaldo I, the Este duchy aimed unwaveringly in the direction of the Empire, thus helping to create a military and political bridgehead that represented a secure base for imperial power in Italy.
When, on 31 May 1708, emperor Joseph I responded to the spiritual remonstrances of Pope Clement XI by ordering general Bonneval to enter Comacchio and to extend the occupation to the entire territory, the ground seemed to have been laid for a happy outcome to the Este claims. But it is clear that the emperor's strategy was not intended so much to further the designs of duke Rinaldo as to reinforce imperial claims to Comacchio and likewise to Parma and Piacenza.
In other words, the Emperor was prepared to cultivate Este interests in order to multiply the doubts and difficulties of the Roman court, but no more than that, while Modena, naturally, had been hoping for a more serious breach between Vienna and Rome.
At this point enter Lodovico Antonio Muratori, by Rinaldo's command summoned from Milan, where he was in charge of the Ambrosiana library, to Modena to reorganize the Este archives and to conduct the major research effort that was to make him famous.
In the course of these labours he found himself in close contact with Gottfried Wilhelm Leibniz, the eminent philosopher and scholar.
Muratori and Leibniz backed up the Estes' arguments, while a counter attack was launched from Rome by monsignor Giusto Fontanini, a master of eloquence who was later to become Bishop of Ancira. Briefly, the Curia's objections were countered as follows: Comacchio was independent of Ravenna; the extent and specific nature of the lands donated in 775 by Pepin to the Church were not clear, while the same held for the relevant juridical guarantees; Charlemagne had continued to rule those lands even after the donation; Comacchio did not belong to the district of Ferrara, but represented a separate juridical entity; in any case, what counted was the fact that the Estes had owned Comacchio without a break from 1325 to 1598; the Estes, who had conquered Ferrara twice, had been elected by the people; Ferrara had been granted to the Estes by Pope Alexander IV as an alodial property, and therefore one that might be passed on by succession; Alfonso I's third marriage was valid, while the Papal occupation of Ferrara in 1598 was illegitimate.
Despite these arguments, the situation moved steadily against the claims of the Estes. And, while it is true that the occupation of Comacchio by imperial forces was to cease only in 1725, it is equally true that Rome managed to have general Bonneval destituted of his command. By that time the game was lost.
Muratori was loath to accept this and, in a letter, he expressed his disappointment in a pithy phrase: «Comacchio is lost. Long live greed and the omnipotence of money!»