Largest town plan

The largest town plan was the Forma Urbis Romae, a map of the capital of the Roman Empire carved on to 150 marble slabs between 203 and 211 CE. The map originally measured 18 m wide and 13 m high (59 ft x 42 ft 7 in), giving a total area of 234 m² (2,518 sq ft), but only fragments (around 10% of the original map) survive.

The plan was carved at a scale of roughly 1:240 (meaning a distance of 1 cm on the map represented 2.4 m in the real world), and depicted the city in enough detail to show not only individual buildings, but also small details like fountains, the locations of columns and even the floorplans of temples and public buildings.

The map was commissioned by the emperor Septimus Severus as part of the restoration work on the Temple of Peace, which was badly damaged by a fire in 192 CE. It was originally mounted to an interior wall in the temple, within a hall large enough to allow visitors to stand back and view the city in its entirety. It is not clear what practical purpose, if any, the map may have served – it was too large to be a functional reference, and lacked measurements and notations used in Roman land-ownership maps. The most widely accepted theory today is that it was decorative.

The map began to deteriorate as the wealth and resources of the Roman Empire declined. At the same time, the practice of Christianity saw the old temples re-purposed or demolished. A church was built in the space adjacent to the temple, with the wall on which the map was mounted becoming the back wall of the church. The slabs of the map either fell off the wall and smashed as the metal pins holding them in place corroded or were removed by Romans looking for building materials.

The map was rediscovered in 1562, when fragments were found on the old temple site. There was a major attempt to gather the lost pieces in the 18th century, and further fragments are periodically unearthed during construction work or archaeological investigations.