In Grado, between 627 and 628, patriarch Fortunatus [Fortunato], who was considered abusive for his non-adhesion to the Roman see and dreaded punishment, after plundering the church escaped into Lombard territory. Since the see of Grado was left devoid of a bishop, on February 18th, 628 pope Honorius I (625-638) under his own authority appointed a Roman sub-deacon, Primogenius, to that cathedra: the latter, dressing the metropolitan pallium, was then ordained by the suffragan bishops of Venetia and Istria. The nomination of a Roman directly decided by the pope, who stepped over local issues, was an extra-ordinary fact, due to the importance Rome, as well as Constantinople, gave to that see for its neighbourhood to the Lombard area. During the seventh century the patriarch in Grado was held as the only legitimated titular of the Aquileian see by the Roman bishop. The epithet of ‘patriarca Gradensis’ the papal see would have given to Primogenius (pope Theodor, between 642 and 647) and to Agathon (pope Benedict II, between 683 and 685) is apparently a later interpolation: in the year 649 Maximus and in 680 Agatho participated in the Lateran synods with the title of episcopus sanctae Aquileiensis ecclesiae. Upon the end of the Lombard reign (774), in order to regain their jurisdiction over Istria – the richest and most important region of the ecclesiastical province – the patriarchs of Grado coped with the Byzantine policy, the new Frankish power and the newborn anti-Frankish and autonomist Venetian duchy. In the Frankish empire milieu, with the ascent of the Patriarchate in Cividale, the synod of Mantua (827) acknowledged the Aquileian bishop as the only legitimated patriarch and demoted Grado to a simple parish of Aquileia. The argument on the Patriarchate of Grado and its metropolitan jurisdiction legitimacy against the Aquileian patriarch’s claims arouse endless disputes and plenty of violence that wore out and impoverished the insular Church. Still in 1053 pope Leone IX ratified that Grado, as a New Aquileia, should have been perpetual chief and metropolis of the whole Venice and Istria, while the Foroiuliensis bishop should have exerted his jurisdiction within the border of the former Lombard territory. In Henry Dandolo’s time (1131-1186) the patriarch moved his residence to Venice, though this was already a diocese having its see at St. Peter of Castello; in 1451 pope Eugene IV suppressed the title of Grado and established the Patriarchate of Venice.
The complicated events of the contraposition between Grado and Aquileia