Leaving St Mark’s Basin and passing the Riva dei Sette Martiri, you cannot ignore two enormous archways in the buildings opposite. My research has failed to find any explanation or purpose for these arcs, though they would allow something pretty large to pass through. What Google will do is to provide you with plenty of opportunities to rent the apartments in those buildings.
They acquired a purpose on one of the days when the thunderstorms arrived however, making an excellent place to shelter. Those beneath them would have been glad of the respite from the rain, though perhaps not as glad as those who rented the apartments.