01The quick answer
The Palazzo Venezia (Italian: [paˈlattso veˈnɛttsja]; 'Venice Palace') or Palazzo Barbo, formerly Palazzo di San Marco ('Saint Mark's Palace'), is a large early Renaissance palace in central Rome, Italy, situated to the north of the Capitoline Hill. Today the property of the Italian Republic it houses the National Museum of the Palazzo Venezia. The main (eastern) facade measures 77 metres (253 ft) in length, with a height (excluding tower) of about 31 metres (102 ft). The north wing, containing the "Cibo Apartment", extending westwards, measures 122 metres (400 ft) in length. It covers an area of 1.2 hectares (2.9 acres) and encloses two gardens and the Basilica of Saint Mark. It was built in the present form during the 1450s by Cardinal Pietro Barbo (1417–1471), titular holder of the Basilica of Saint Mark, who from 1464 ruled as Pope Paul II. Barbo, a Venetian by birth as was customary for cardinals of the Basilica of Saint Mark, lived there even as pope and amassed there a great collection of art and antiquities. During the first half of the 20th century it became the residence and headquarters of Benito Mussolini, dictator of Fascist Italy (1922–1943), who made notable orations from its balcony to huge crowds filling the Piazza Venezia.
02How it came to be
The original structure of this great architectural complex consisted of a modest medieval house intended as the residence of the cardinals appointed as the titular holders of the Basilica of Saint Mark. In 1469, having undergone a massive extension, it became a papal residence and in 1564 Pope Pius IV, in order to win the sympathies of the Republic of Venice, of which the patron was Mark the Evangelist, gave the mansion to the Venetian embassy to Rome on condition that part of the building would remain a residence for the cardinals of the Basilica of Saint Mark, which part is now known as the Cibo (or Cybo) Apartment, and that the Venetian Republic would provide for the building's maintenance and future restoration. The main eastern facade of the palace faces Piazza Venezia and the north wing, containing the Cibo Apartment, forms part of the south side of the Via del Plebiscito.
03The detail most people miss
It was rebuilt in 1451 when owned by Cardinal Pietro Barbo (1417–1471) who from 1464 ruled as Pope Paul II (1464–1471), a nephew of Pope Eugenius IV. It became a fortified building, composed of a half-basement and a mezzanine which functioned as a piano nobile. In 1455, Pietro Barbo had a commemorative medal struck to mark its construction. The building manifested some of the first Renaissance architectural features in Rome although the overall aspect is of a massive, fortified medieval structure with battlemented parapet. On its west side it adjoins the ancient Basilica of Saint Mark, which is aligned south to north, founded by Pope Marcus in 336 and dedicated to Mark the Evangelist who would become protector of Venice, completely rebuilt in 833, and which underwent frequent reconstructions since then. Much of the stone to build the Palazzo was quarried from the nearby Colosseum, a common practice in Rome until the 18th century. The design is traditionally attributed to Leone Battista Alberti.