Piazza Venezia is not only the topographical center of Rome but its historical locus as well. It forms the nexus between Rome's various historical periods - joining ancient Rome with the Rome of the Popes. It is hands down the most important piazza in Rome- the Capital of Italy- rendering it Italy's center.
The piazza was finally completed in the early 20th century with the construction of the Vittoriano, the monument to King Victor Emanuel.