It is amazing what one discovers when one looks! Would you believe that there is an "International Catacomb Society" (almost as esoteric as the "Labyrinth Society" which led to the prayer Labyrinth connection!)?
Els and I had problems when looking at "funerary connections" in determining the exact definition of the various words used to describe such locations (Mausoleum, Ossuary, Necropolis, Hypogeum, Catacomb, Cemetary, Tomb etc). Some of these words appear to be used interchangeably or can be subsumed within another. So I rather hoped to gain an insider definition of a "Catacomb" from the Society (E.g. when is a Catacomb a Hypogeum or v.v. etc??). In fact the Society's web page doesn't define Catacomb but does define "Hypogeum" as "usually found below living quarters, an underground chamber used as a tomb".
So it was back to Wiki. It suggests that the word "Catacomb" is used to describe underground man made "caves"/galleries/passages containing Christian Tombs and that Hypogeum is reserved for pre-Christian underground tombs. Yet elsewhere it is clear that "Catacomb" can also be used for non-Christian examples - eg Jewish and even Bronze Age. However, since the word originally came from its specific use in a specific location in Rome, all uses of the word for earlier and later examples must be "derivative" from that example.
In the end Els/I decided on grounds of "common practice" to use whatever word was used in UNESCO documentation to describe the location. But that of course doesn't solve the problem where the documentation doesn't mention the location but we still know that there is one inside the inscribed area or where 2 different words are used in different sources!
So are there other potential "Connections" for "Catacomb"? In fact Wiki lists a fair number of "Catacombs" and also some "Catacomb-like" structures. Using the rule that "if it is called a Catacomb it is one" there would appear to be at least 2 further locations within WHS boundaries. I have double checked with tourist Web sites describing the building and both are open to view and are called "Catacombs" locally
a. Vienna - Under St Stephens Cathedral
"The Catacombs. Take the guided tour below ground, and you'll see the usual assortment of sarcophagi holding the bones of dead rulers, archbishops, and other personages. Somewhat stranger are the bronze containers where kidneys, livers, etc. of Habsburg emperors were interred in what might be called an undertaker's waste dump. Finally, you'll explore the catacombs where the bones of more than 15,000 Viennese have been stacked like kindling since the 1700s. "
b. Lima - Under San Fransisco Convent
"Catacombs: Discovered in 1943, they countain thousand of skulls and bones, serving as a burial-place until 1808, when the city cemetery was opened outside Lima. It is estimated that 25,000 bodies were laid to rest there; the crypts, build of bricks and mortar are very solid and have stood up well the earthquakes, it is also believe that existed secret passageways connected to the Cathedral and the Tribunal of the Holy Inquisition."
A 3rd possibility is Trier. Although these are described as "Catacomb-like" by Wiki some tourist info clearly states that there are "catacombs" beneath the Imperial Baths - can anyone confirm??
As far as I can see all other possibilities are excluded. The Catacombs of Rabat Malta are on Malta's T List. The Parisian Catacombs (also called the "Municipal Ossuary"!!) do not appear to be within the "Banks of the Seine" boundaries