The Milan tramway network () is part of the public transport network of Milan, Italy, operated by Azienda Trasporti Milanesi (ATM). In operation since 1881, the network is currently long, making it one of the biggest in the world. It has the unusual track gauge of (Italian gauge), and comprises 17 urban lines. While the Milan metro is characterized by a low level of centrality, with no more than two lines ever crossing each other at any of the interchange stations, the tram network is substantially centralized, with nearly half of the lines passing or terminating around Piazza del Duomo, the city central square. History Horses and steam (1876–93) Following the establishment of omnibus services in 1841, Milan acquired its first trams on 8 July 1876, upon the inauguration of the Milan–Monza tramway, which was operated by animal traction. The terminus of this line was at Porta Venezia, outside the city limits. On 24 June 1877, a second tramway was opened between Milan and Saronno, with a terminus at Arco della Pace. After only a few months, the city government agreed to the laying of rails in the city. The line from Monza was therefore extended up to Piazza San Babila, and the line from Saronno through Piazza d'Armi to Via Cusani, inside the city limits. A year later, on 6 June 1878, Milan's first steam tramway, to Vaprio, started operations. The success of this line made steam power popular. The existing line to Saronno was therefore extended (1878), and new lines were constructed to Sedriano (1879), Vimercate, Pavia and Lodi (1880), Giussano (1881), and elsewhere. These lines did not form a single network, but were awarded to different companies, and were operated from different termini. Milan's first urban tramway network, with animal traction, was opened in 1881, at the National Exhibition. This network was laid out radially, with a central terminus in Piazza del Duomo, and lines heading out towards the city gates. It was managed by the Società Anonima degli Omnibus (English: Omnibus Public Limited Company) (SAO). The Edison era (1893–1917) In 1892, the Edison company presented a project for the electrification of the urban tramway network. The first stage of this project was an experimental line from Piazza del Duomo to Corso Sempione through new residential areas, to demonstrate the advantages of the new system. A year later works started on the rest of the project. By