Among the particularities that distinguished the doge from all the other sovereigns there was also his headdress: in fact, he did not wear the crown but the horn, a kind of cap of Byzantine origin that took different forms in the various eras.
Initially it imitated the cap of the Eastern emperors in the shape of a slightly prolonged cap, then between the 11th and 12th centuries it was divided into two parts by a bow or a round button and finally, in the 13th century, it assumed the shape of the horn, first pointed and then rounded.
Over time it was called in different ways (biretum, corona, horn or zogia) and the fabric with which it was made also varied: it was of shamite fabric in gold and silver, of scarlet cloth, of damask, of crimson velvet, of white tabì, of white silk or other fabrics with ornaments of rare skins, gems, pearls and gold.
During the tour of the square after the election and in minor meetings, the doge wore the common horn, a cap made of the same fabrics as the ceremonial horn and sometimes decorated with fur. Sometimes he would put a leather-lined brocade hood over it, probably to protect himself from the cold.
After the twelfth century, the doge wore a kind of very fine cloth bonnet under the horn, similar to the papal camauro, tied or unfastened under the chin, according to the epochs, which was not removed even during the elevation in the church.
It was the younger councilor who put the camauro on the doge's head while it was up to the older councilor to put the horn on him saying: "Accipe coronam ducatus Venetiarum". The two hats were taken from the treasury of San Marco by a procurator of San Marco and two of his ministers who presented them respectively placed in a saucer and in a gold cup.
The horn was worn, in a smaller form than that of the doge, also to crown the golden veil of the dogaressa his wife.
Over time, the ducal horn was embellished with inserts in damask, pearls and precious stones.
Disappeared with the fall of the Republic, it still stands out in the coat of arms of the City of Venice, replacing, by presidential concession, the traditional city walls.
The writer Giustina Renier Michiel, nephew of the doge Paolo Renier (1779-1789), in her book "Origine delle feste veneziane", tells that it was the abbess of the convent of San Zaccaria, Agostina Morosini, who had the idea of giving the doge a preciously embroidered horn:
... At the time that Agostina Morosini was Abbess in San Zaccaria, that is to say the year 855 - he writes - Pope Benedict III was in Venice and visited that church and monastery. Deeply admired for the virtue and holiness that he saw reigning among those sacred virgins, he wanted, on returning to Rome, to give testimony of his satisfaction by enriching them with a large number of relics and indulgences.
It was then that the doge Pietro Tradonico (836-864), whose family was later called Gradenigo, began to visit the church of San Zaccaria in the ever-increasing presence of the people. In fact, the head of the Republic could not avoid attending the most important religious ceremonies. Easter was therefore established as the most suitable day for the annual visit of the Serenissimo to the church of San Zaccaria.
The Abbess Morosini happy and honored in seeing the doge go in procession to his church, offered him, in agreement with her nuns, a gift worthy of him, and of the rich heritage he enjoyed. It was all gold - continues Renier Michiel - it was decorated with twenty-four oriental pearls in the shape of pears. On the top shone a diamond with eight faces, of a weight, and of an admirable luster. In front of it a ruby also of maximum thickness, which dazzled with the vivacity of its color and its fire.
How then to describe the great cross that was in the middle of the diadem? This was made up of precious stones, and particularly of twenty-three emeralds, of which five, which form the cross, won out in beauty what can be seen in this genre.
Such an inestimable gift was greatly appreciated by the Doge and from that moment it was established that the superb diadem was not to be used except for the day of the coronation of the new Doges. But so that those good religious were not completely deprived of the pleasure of seeing him again (a pleasure that recalled a most noble action of that community), it was also decreed that every year on the day of the visit to be made to San Zaccaria, it would be taken from the public treasure, and on a basin presented to the Doge himself and shown to all the nuns, which was always exactly executed ... "
They then wanted to give the Feast, or rather the visit of San Zaccaria, a more decorous aspect, and therefore it was decided that "the Doge with the Signoria, instead of going on foot, would go to the monastery in his golden boats, and that large brotherhoods would be found at that time in the church. The crowd of the people grew then, and continued afterwards until the year 1796, yes to acquire the assigned indulgences and yes to want to admire that diadem that with its splendor dazzled everyone's eyes ".
In the year 864, the doge's visit to the Sisters of San Zaccaria ended in tragedy: at the end of the ceremony, Pietro Tradonico was assassinated.
For a long time the city was torn by dissensions between some noble families who, divided into two factions, clashed daily so much that Venice seemed to have become a battlefield. Tradonico's attempts to reconcile spirits were interpreted as an ambiguous attitude: the unrest was growing rather than decreasing and the doge was accused of being an unjust tyrant. On Easter day in the year 864, upon leaving the church of San Zaccaria, he was attacked and killed with a dagger.
Following this episode, the citizens gathered in an assembly and decided to elect three Commissioners who punished the guilty and supervised to prevent any riots and also controlled the conduct of the doge. Over time this magistracy was made permanent and its members were called Avogadori di Comune.