Focus on Barbarigo Altarpiece and explain the Ex-voto.
In Venice it became the custom in the Renaissance for the higher officials, beginning with the Doge, to commission (at their personal expense) an ex-voto painting in the form of a portrait of themselves with religious figures, usually the Virgin or saints, in thanks for achieving their office. For lower officials only their coat of arms might represent the official. The painting was hung in the public building where they worked or presided.Aspects of the picture hint at what many contemporaries saw as the excessive self-aggrandizement of the Barberigo brothers. Rather being presented to the Virgin and Child by his name-saint Augustine, as was usual, the Doge is presented by Saint Mark, patron saint of the Venetian Republic, as well as Marco Barberigo.  Instead of looking towards the Child, the Doge looks out towards the Venetians passing the painting. There was opposition to hanging it in the Doge's Palace, which may be why Barberigo instead bequeathed it to a convent (so probably saving it from a later fire).  Before this it apparently hung in his home, the Palazzo Barbarigo Nani Mocenigo (which survives; not the Palazzo Barbarigo).In 1501, already dying, Agostino left the canvas to the nunnery of Santa Maria degli Angeli in Murano to be its high altarpiece, but it was soon moved from there (to make room for Titian's Annunciation) to San Pietro Martire. Vasari mentioned it as being in San Michele di Murano but probably mistook it for another Bellini work, now lost, which was already in the Cappella della Santissima Croce in the church of the Camaldolese.
Palazzo Barbarigo Ex-voto Venetian Republic Doge Murano Marco San Pietro Martire Titian Doge's Palace Palazzo Barbarigo Nani Mocenigo Saint Mark ex-voto Santa Maria degli Angeli Camaldolese San Michele di Murano Vasari