When I have some free time between one lesson and another one, I like to relax on the sidebands of Tre Archi Bridge. Located in the Cannaregio residential zone, the bridge has an atypical, unique-in-Venice form: a central arch and two smaller ones on the sides while all the other bridges in Venice were made of just one big arch connecting one bank to the other one.
This shape reduces access to larger vessels and maybe this is the same reason that the bridge was built as a bottleneck, to prevent access to large enemy boats from the less defended side of the city. Still, it is more likely that the choice came simply from stylistic reasons and static in order to avoid heavy solidification at the bases of the fondamenta, shifting the weight on the central pylons.
The Tre Archi Bridge, however, also represented the only gateway to the city for travelers who came from the mainland. First built with wood and then restored with stone the bridge was built without sidebands, as indeed were many bridges in Venice, added during the renovation work with a total different style that looks funny and charming at the same time, making it, in my opinion, one of the nicest bridges of the city!