Old Vatican

Rodolfo Lanciani, Forma Urbis Roma (Milan, 1893-1901), plate VI - The Vatican Gardens (North) (Vatican Museums)

Rodolfo Lanciani, Forma Urbis Roma (Milan, 1893-1901), plate XII - The Vatican Gardens (West)

Rodolfo Lanciani, Forma Urbis Roma (Milan, 1893-1901), plate XIII - St Peter`s, The Vatican

Rodolfo Amadeo Lanciani 1846 - 1929  was a very distinguished and celebrated Professor of Ancient Topography at the University of Rome from 1878 until 1927

He was a pioneer, one of the four founders of a rational, modern approach to Roman cartography and archaeology 

He was supervisor of excavations in the city. He was also a prolific author

He was a member of two academies, dei Lincei and di S. Lucia, as well as the recipient of many honorary degrees from many famous universities including Oxford and Harvard

His Forma Urbis Romae has been described as ‘a magnificent map of the city and a marvellous example of cartography as well as an encyclopaedia of typographical information. It is still an essential tool for anyone working on the ancient city’ (L. Richardson, A New Topographical Dictionary of Ancient Rome [John Hopkins, 1972], xxv). 

The forty-six maps of the Forma Urbis have a scale of 1:1,000. 

Overlaid on the network of modern streets and buildings are the known remains of ancient Rome. 

The work is said to be unsurpassed to this day.

Major parts of the 46 plates are present here (in high resolution) and more be seen here in much lower resolution

From the maps above one can see the many layers of Rome in and around the Vatican where most Catholic tourists who visit Rome will head at least once.

One can see that the Basilica is built right on top of the old Roman road the Via Cornelia

The title of Lanciani`s work  is of course more than a hat tip to the  Forma Urbis Romae or Severan Marble Plan, the  massive marble map of ancient Rome, created under the emperor Septimius Severus between 203 and 211. 

It originally measured 18 m (60 ft) wide by 13 m (45 ft) high and was carved into 150 marble slabs mounted on an interior wall of the Temple of Peace.

For some assistance in deciphering Lanciani`s maps you might wish to consult Samuel Ball Platner A Topographical Dictionary of Ancient Rome London : Oxford University Press, 1929

This is on Bill Thayer`s great website Lacus Curtius

Here are the entries for the Via Cornelia and the Vatican from the classic 1929 work: