Surrounded by palazzi with large porticoes in the 19th-century style, the piazza was built by
Gaetano Koch shortly after the
unification of Italy. Umbertine in style, it is the largest piazza in Rome (316 x 174 metres). In the centre of the piazza is a garden with the remains of a fountain built by
Alexander Severus (so called
Trophy of Marius), and the
Porta Alchemica (''Alchemist's Portal
or also called Magic Gate or Porta Magica''), the entrance to Villa Palombara, former residence of the
alchemist Marquis Palombara. ==Cultural references==