In 1339 the city's leaders launched a plan to enlarge the cathedral and create one of Italy's largest places of worship. Known as the Duomo Nuovo, the remains of this unrealised project are on Piazza Jacopo della Quercia, at the eastern side of the main cathedral. The daring plan, to build an immense new nave with the present cathedral becoming the transept, was scotched by the plague of 1348.
The cathedral's interior is truly stunning. Walls and pillars continue the black-and-white-stripe theme of the exterior, while the vaults are painted blue with gold stars. High along the walls of the nave is a long series of papal busts. After looking up, look down…and you'll see the cathedral's most precious feature - the inlaid-marble floor, decorated with 56 glorious panels, by about 40 artists over the course of 200 years (14th- to 16th-centuries), depicting historical and biblical subjects. The older, rectangular panels, including Ruota della Fortuna (Wheel of Fortune; 1372) and Lupa senese e simboli delle città alleate (The She-Wolf of Siena with the emblems of the confederate cities; 1373) are graffiti designs by unknown artists, both restored in 1864, created by chiselling into white marble and filling the holes with bitumen or mineral pitch. Domenico di Niccoló dei Cori was the first known artist to work on the cathedral, contributing several panels between 1413 and 1423, followed by renowned painter Domenico di Bartolo, who contributed Imperatore Sigismundo in trono (Emperor Sigismund Enthroned) in 1434. It wasn't until the tenures of director Alberto Aringhieri (1480-1504) and celebrated Sienese artist Domenico Beccafumi (1518-47) that the floor scheme saw swift, dramatic expansion. These later panels were done in more advanced multicoloured marble, inlaid with hexagon and rhombus frames. Unfortunately, all but a few are obscured by unsightly, protective covering, revealed only from 7 to 22 August each year. Seek out the exquisite 13th-century marble and porphyry pulpit by Nicola Pisano, who was aided by his equally talented son, Giovanni. Intricately carved with vigorous, realistic crowd scenes, it's one of the masterpieces of Gothic sculpture. You can't inch as close as you might like as barriers keep you at a respectful distance. To shed a little light on the subject, stick coins into the machine (around €1.50 gets you a generous minute of illumination). Other significant works of art include a bronze statue of St John the Baptist by Donatello, situated in a chapel off the north transept.
