San Todaro—who is either Saint Theodore of Amasea or Saint Theodore Stratelates, no-one seems to know or care—was the first patron saint of Venice from its foundation. However, in the year 828, 407 years after Venice’s foundation, the body of Saint Mark was brought to the city from Alexandria in Egypt and he became the new patron. Since Saint Theodore was mostly venerated by the Greek Orthodox Church, based in Constantinople, this was probably an attempt by Doge Giustianiano Participazio to assert Venice’s independence from Constantinople.
Todaro continued to be venerated in Venice, just to a lesser degree, and after the Venetians sacked Constantinople in 1297, his body was brought to Venice and placed in the church of San Salvador, which is next to the Scuola Grande di San Todaro.
A statue of San Todaro is atop one of the twin columns in the Piazzetta di San Marco, the other being surmounted by a lion of Saint Mark. It was between these two columns that unhappy criminals were executed, hence the Venetian phrase, esser tra Marco e Todaro, which can be translated as ‘being between a rock and a hard place’.