Porta San Marco, Customs gate in the Leopoldine customs wall, Livorno, Italy.

Porta San Marco is a city gate within the Leopoldine Walls in Livorno and features a stone arch entrance with two semicircular structures on each side. The exterior displays rusticated stonework, and interior rooms once served as inspection areas for customs officials.

Porta San Marco was built between 1839 and 1840 under Carlo Reishammer, replacing the older Rivellino di San Marco gate. It was part of the Leopoldine Walls begun in 1835 by Alessandro Manetti, when the free port's customs boundary was extended beyond the Fosso Reale. In 1849 the gate saw fighting between Livorno's inhabitants and Austrian troops, and from 1881 tram rails passed through it.

The gate is topped by a marble Lion of Saint Mark carved by Lorenzo Nencini, and its two semicircular flanking bodies carry marble bas-reliefs. Nearby stand a plaque and a bust of Enrico Bartelloni, commemorating Livorno citizens who died in the 1849 Risorgimento uprisings.

The gate sits near the former Stazione Leopolda and is easily accessible via surrounding streets. Visitors can freely explore the passage and view the architectural details from both outside and inside.

Inside the gate, the rooms once used by customs officers are covered by a cast-iron vault carried on slender metal columns. In Reishammer's design the iron is both structure and ornament, an early use of the material in an Italian public building.