of metal called the fèro (iron). Its shape has evolved through the centuries, as documented in many well-known paintings. Its form, topped by a likeness of the Doge's hat, became gradually standardized, and was then fixed by local law. It consists of six bars pointing forward representing the sestieri of the city, and one that points backwards representing the Giudecca. A lesser-known boat is the smaller, simpler, but similar, sandolo. Waterways Venice's small islands were enhanced during the Middle Ages by the dredging of soil to raise the marshy ground above the tides. The resulting canals encouraged the flourishing of a nautical culture which proved central to the economy of the city. Today those canals still provide the means for transport of goods and people within the city. The maze of canals threading through the city requires more than 400 bridges to permit the flow of foot traffic. In 2011, the city opened the Ponte della Costituzione, the fourth bridge across the Grand Canal, which connects the Piazzale Roma bus-terminal area with the Venezia Santa Lucia railway station. The other bridges are the original Ponte di Rialto, the Ponte dell'Accademia, and the Ponte degli Scalzi. Public transport Azienda del Consorzio Trasporti Veneziano (ACTV) is a public company responsible for public transportation in Venice. Lagoon area The main means of public transportation consists of motorised waterbuses (vaporetti) which ply regular routes along the Grand Canal and between the city's islands. Private motorised water taxis are also active. The only gondole still in common use by Venetians are the traghetti, foot passenger ferries crossing the Grand Canal at certain points where there are no convenient bridges. Other gondole are rented by tourists on an hourly basis. The Venice People Mover is an elevated shuttle train public transit system connecting Tronchetto island with its car parking facility with Piazzale Roma where visitors arrive in the city by bus, taxi, or automobile. The train makes a stop at the Marittima cruise terminal at the Port of Venice. Lido and Pellestrina islands Lido and Pellestrina are two islands forming a barrier between the southern Venetian Lagoon and the Adriatic Sea. On those islands, road traffic, including bus service, is allowed. Vaporetti link them with other islands (Venice, Murano, Burano) and with the peninsula of Cavallino-Treporti. Mainland The mainland of Venice is composed of 5 boroughs: Mestre-Carpenedo, Marghera, Chirignago-Zelarino, and Favaro Veneto. Mestre is the centre