Every one knew how laborious the usual Method is of attaining to Arts and Sciences; whereas by his Contrivance, the most ignorant Person at a reasonable Charge, and with a little bodily Labour, may write Books in Philosophy, Poetry, Politicks, Law, Mathematicks and Theology, without the least Assistance from Genius or Study.

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Laputan Logic*
Fanciful. Preposterous. Absurd.
The Marble Plan

Posted on Monday 12 January 2004


A fragment of the Forma Urbis Romae



Part of the Circus Maximus including the Arch of Titus
While the Forma Urbis Romae, a city plan of third century Rome, may not have been the oldest street directory in the world, it must surely rank as one of the most extradordinary.

The plan was enormous, measuring over 18 metres in length and more than 13 metres in height (60 x 43 feet) and big enough to cover an entire wall inside the aula (main room) of the Templum Pacis in Rome. It was made of carved marble slabs 70 mm thick and would have weighed over 40 metric tons.

It was also astonishingly detailed, depicting all of the architectural features of the city at the time including all public buildings, monuments, palaces, temples, markets, streets, shops and private houses, all at a scale of 240 to 1. Third century Rome, with a population of over one million inhabitants, was unquestionably the largest city in the world and it lost that title only after being finally overtaken by London in the 1800s.

Unfortunately for the plan, as with so many treasures of antiquity, it was destroyed during the Middle Ages and over the following centuries the slabs of marble were robbed as a ready source of building materials. Slabs that hadn't been stolen eventually fell off the wall (now the outer wall of a church) by themselves only to be buried in pieces at its base.

In the sixteenth century, fragments of the plan were rediscovered and the renewal of interest in ancient Rome that began with the Renaissance stimulated the search to find more pieces. Eventually about fifteen percent of the plan was recovered but, alas, it was broken up into a 1,186 individual pieces. A lot of work, mostly done by Italian scholars, has gone into identifying pieces of the plan . Coupled with detailed surveys of ancient sites in Rome, this has led to some impressive results in reconstructing and understanding the plan. Nevertheless, there remain a great many pieces which have defied all attempts at identification and the positions of most of the recovered fragments still remain a mystery. The fragmented Forma Urbis Romae today constitutes one the most challenging jigsaw puzzles in the world.



Fragment of the Subura neighborhood on the Oppian hill.
In an effort to facilitate further reconstruction of the plan, Stanford University has established an online database of the fragments that they have scanned in three dimensions. Currently only 24 fragments are available for viewing on the web but they hope to have the entire set of pieces (warning: 2.2 MB file) processed and available to the general public some time in 2004. The longer term goal of this initiative is to develop computer algorithms in order to search for matches in the jagged edges of the pieces and eventually to automatically find the correct ways to orient the fragments and to put them back together again. When you consider that this is a three dimensional problem (because many of the pieces do not have a front or back face), it's reasonable to surmise that it's going to be fairly hard.

Looking now at some of the pieces, consider a fragment which has been code named 10g. This 80 cm x 40 cm piece weighs more than 30 kilograms and has been identified as a large section of the neighbourhood of Subura including a major street named Clivus Suburanus. The dots in this fragment indicate colonnaded buildings, for example, the dots near the centre of the fragment was a bathing complex.

Subura was a lively commercial and residential district which was a home to a wide range of individuals from caesars and senators to artisans and prostitutes. Poets Martial and Juvenal described the Subura as a sordid commercial area which was riddled with violence, "was dirty and wet"," a resort of harlots", of dealers in provisions, delicacies and finery and of tradesmen of various sorts.

To see how this fragement fits into what is already known about ancient Rome, I have rotated the fragment to use the more familiar North-to-the-top orientation (the Romans used to have South-East at the top of their maps) and placed it over an archaeological survey map of the city made by Rodolfo Lanciani in 1901.

Subura was also once home to Julius Caesar and Augustus built a public portico there and dedicated it to his wife Livia in 7 B.C. The rectangular colonnaded outline of the Porticus Livae can be seen on the fragments in the lower left corner of the image below. Unfortunately, no archaeological trace of this building has ever been found but its existence and location has been attested to by many ancient authors. In a southern fragment adjoining the portico, one can see the a tiny section of the wall that surrounded the expansive grounds of the Thermae Traiani (the Baths of Trajan).

Zooming out even further, I have superimposed the above image over Lanciani's city overview drawing. Here you can see where Subura was located relative to the rest of the city and you can also get a sense of just how small this group of fragments is when compared to the rest of the Forma Urbis Romae plan.


The oval shape below and to the left of Subura is the Amphitheatrum Flavium, better known as the Colosseum, and west of this lay the Sacre Via. Slightly to the north of this was the Templum Pacis, the original home of the Forma Urbis Romae itself (see this zoomable map for more detail).

See also:
History of the Marble Plan
Scanning the fragments of the Forma Urbis Romae
Carving and breaking marble slabs
Analyzing the fragments of broken marble slabs
Computer Scientists Tackle 1600-Year-Old Jigsaw Puzzle
(note that this Society for Industrial and Applied Mathematics article has a basic problem with arithmetic, the plan is more like 1800 years old!)