And on to the last category:

Ancient Rome (24)
http://www.worldheritagesite.org/categories/category64.html

El Jem
Aquileia
Arles
Baalbek
Bosra
Djemila
Dougga
Limes
Romuliana
Leptis Magna
Merida
Orange
Pompeii
Pont du Gard
Lugo
Segovia
Syracuse
Tarraco
Timgad
Tower of Hercules
Trier (better under urban continuity?)
Villa Adriana, Tivoli
Villa Romana del Casale
Volubolis

Have visited 19 of the 24. A few outstanding ones plus a lot of towns containing much the same structures. Some as complete archaeological sites and others with "bits" peeping through among modern cities. 6 are from N Africa. Somehow need to identify the real "gems" among these. Some other sites we have considered earlier are really "Roman" too - e.g the "Phoenician" ones. We just need to do a recheck when the final list is being put together to minimise duplication. And then there is Rome also to cover a lot of "Roman" aspects.

-El Jem - NO - its theatre really is very fine but I wouldn't put it above others as a complete site.
-Aquileia - NO - is rather more than a "Roman" town with its Basilica. Doesn't get it on its Roman aspects
-Arles - NO - Another European town with a theatre, amphitheatre etc.
-Baalbek - YES - For its Temple architecture
-Bosra - NO - another theatre etc etc
-Djemila - NO -nicely situated in the mountains and very "complete" but doesn't push its way in ahead of other N African sites
-Dougga - NO -"best preserved small roman town in N Africa" -but does it really add anything to Leptis?
-Limes - YES - despite the ridiculous "extensions" of every ditch and mound which are being added across Europe (and later beyond?)
-Romuliana - NO - more palaces and temples
-Leptis Magna - YES -We need at least one "North African" site - this certainly makes it for its excellent preservation (at least before recent events)
-Merida - NO - Another set of remains peeking up among the modern town - but nothing that special (except the superb new museum!!)
-Orange - NO - Primarily an arch and a theatre- it may be the "best preserved in Europe" but we have plenty of others
-Pompeii - YES - for the absolute uniqueness of its preservation
-Pont du Gard - YES - a tough choice between it and Segovia but I don't think both are justified
-Lugo - NO - A nice "complete" wall but not enough
-Segovia - NO - its Aqueduct is very fine but I will stick with the Pont du Gard
-Syracuse -NO - As with Trier am not really sure that this should be here as its Roman aspects are not as important as its other aspects (Greek etc)
-Tarraco - NO - yet another set of Roman town ruins set among a modern town
-Timgad - MAYBE - if one looks for "something different" then this very "complete" site planned on a pure grid pattern and with lots known about the owners of individual houses seems a possible choice
-Tower of Hercules - NO - Interesting monument but a lot of neo-classical restoration - not strong enough as a single structure to make it IMO.
-Trier (better under urban continuity?) -MAYBE - A fear I may be accused of undervaluing it. It is interesting that its Roman remains have survived and e.g the Porta Negra has a certain iconic status but does it really add anything to others?
-Villa Adriana, Tivoli - YES - for its completeness and the quality of its architecture
-Villa Romana del Casale - YES - can we really have both this and Adriana? They are different of course but can anyone else distinguish one as being "better" than the other?
-Volubolis - NO - yet another nice N African ruin but nothing special enough to mark it out?

Following the statements above my selection would differ on some sites:

Arles: Y It's not only the Roman monuments which make up for this rather complete site, the Romanesque monuments add to it. Like I said before, it would make my personal 200 anytime and since it didn't make my medieval European selection this should be the place to include it. I would certainly rank it (overall) above Trier. (despite the Roman gate)

Pont du Gard/Segovia: Although the aquaduct of the Pont du Gard is pictureperfect I would prefer Segovia. Mainly because Pont du Gard is only one monument and Segovia is so much more

Villa Adriana/Romana del Casale; I'm not sure of Adriana but I would include Romana del Casale because of its magnificient mosaics. Is there a site where these mosaics are more complete and in their original place?

I visited 12 out of the 24.

Considering other categories such as Asian, Subindian continent, Greek, Egyptian got quite a fair share of sites, I wouldn't leave out so many Roman monuments and sites as others before me did for one the most important empires and civilisations in the world.

My selection:
El Jem (Maybe , it wouldn't make my top 200 probably but as an Arabian site I would choose it among the top 400)
Aquileia (one of the best examples of mosaic remains around)
Villa Romana del Casale (same as above depicting everyday life in Ancient Rome)
Baalbek (temple architecture)
Leptis Magna (one of the best examples in North Africa)
Pompeii (unique)
Pont du Gard (best example of Roman aqueduct)
Segovia (best example of aqueduct still integrally forming part of a modern historic centre)
Trier (best example of several Roman sites within the same city and iconic)
Villa Adriana (best example of a "Roman Villa")
And obviously Rome!

I choose:
El Jem - another typical well preserved Roman town with fine Theatre -- NO
Aquileia - beautiful mosaic ruins, but many Roman sites can represent mosaic and Roman in the same time -- NO
Arles - Roman mounments here is not significant -- NO
Baalbek - Beautiful and really stunning -- YES
Bosra - another typical Roman ruin -- NO
Djemila - regional significant -- NO
Dougga - another typical well preserved Roman town -- NO
Limes - Hadrian wall is really nice but cannot compare to Great Wall of China in the same category -- NO
Romuliana - another ruins of Roman palace -- NO
Leptis Magna - Best Roman town to represent whole N Africa -- YES
Merida - another typical roman ruins in modern city -- NO
Orange - Beautiful theatre and that's all -- NO
Pompeii - Really unique site to study Roman life -- YES
Pont du Gard - the mother of all Aqueduct -- MAYBE
Lugo - Nice and complete Roman Wall, partial ruins in Rome or istanbul are more impressive -- NO
Segovia - another nice aqueduct similar to many towns -- NO
Syracuse - Too much Greek to be consider Roman -- NO
Tarraco - another but munimal ruins in modern city -- NO
Timgad - interesting sites -- MAYBE
Tower of Hercules - I still question its authenticity -- NO
Trier (better under urban continuity?) - Only Porto Nigra impress me for Roman ruins -- NO
Villa Adriana, Tivoli - very big palace ruin but I am not impressed at all, too similar to Rome -- NO
Villa Romana del Casale - Bikini girl mosaic? -- NO
Voloboris - another Roman ruins city -- NO

This one needs a summary.

Summarizing.
Would like to see more opinions here
Do we think this is an overrepresented category? Sites like Palmyra and Ephesus also have large Roman components.

El Jem
Aquileia
Arles
Baalbek - stunning temple architecture
Bosra
Djemila
Dougga
Limes
Romuliana
Leptis Magna - Best Roman town to represent whole N Africa
Merida
Orange
Pompeii - unique site to study Roman life
Pont du Gard - best example of Roman aqueduct
Lugo
Segovia - best example of aqueduct still integrally forming part of a modern historic centre
Syracuse
Tarraco
Timgad
Tower of Hercules
Trier (better under urban continuity?)
Villa Adriana, Tivoli - best example of a "Roman Villa")
Villa Romana del Casale - mosaics depicting everyday life in Ancient Rome
Volubolis

Plus (brought over from different category):
Rome

As is the case with Christian sites and architecture, Ancient Rome is quite overrepresented in the WH list. Yet, I believe we mustn't put it on par with other minor civilisations. Its huge significance in history warrants in my opinion having more Ancient Rome WHS.

I want to divide into 2 sub-categories.

In europe

Baalbek - YES - For its Temple architecture
Pompeii - unique site to study Roman life
Segovia - best example of aqueduct still integrally forming part of a modern historic centre
Villa Romana del Casale- richest, largest and most complex collection of Roman mosaics in the world
Rome

In North Africa

Dougga - African Mosaic
Leptis Magna- Best African site
El Jem- Most recognizable monument in Roman Africa

I think this category is not well discussed. (only 5 votes till now). We can wait for others to vote before making the summary.

My votes:

Baalbek Fantastic preservation, incredible architecture and the influence on architecture through the ages is extremely important - highly influential on Renaissance and neo-classical artists. One of the first sets of drawings to reach the North was of Baalbek and was a spark to neoclassicism.

Limes Hadrian's Wall - mainly.

Pompeii/Herculaneum This one is perhaps the most important. The art-history/archaeological importance of this can not be overstated. Furthermore it gives a look into everyday Roman life.

Pont du Gard Iconic and monumental. Evokes the unrivaled glory of Roman civic works.

Leptis Magna IMO, the best Roman site in Africa.

Villa Romana del Casale Mosaics.

Villa Adriana, Tivoli Again, the importance of this site can't be stressed enough in the development of the countryside villa as we know it and the later developments of that. As a site to visit, it is extremely interesting.

Are we voting for Rome here? If so, add that as a YES too.

I wish Maison Caree in Nimes was listed already, because that would be a solid YES.

Maybe:
El Jem - I think ampitheatres are covered by other sites, but I do find this one really impressive. Rome has the Colosseum of course. Do we need another? (Arles, El Jem, Verona, Tarragona, Merida, Orange, etc.)

P.S. Why isn't Italy fixing up its Ostia nomination? That is such a crucial site and I think the WH List is all the poorer for it not being included. Other than Scrovegni Chapel, Italian sites lately have not been up to the level of a site like Ostia.

Summarizing again, and bringing these over to the main summary page

El Jem - Amphitheatre is most recognizable monument in Roman Africa
Aquileia
Arles
Baalbek - stunning temple architecture
Bosra
Djemila
Dougga
Limes - mainly for Hadrian's Wall
Romuliana
Leptis Magna - Best Roman town to represent whole N Africa
Merida
Orange
Pompeii - unique site to study Roman life
Pont du Gard - best example of Roman aqueduct
Lugo
Segovia - best example of aqueduct still integrally forming part of a modern historic centre
Syracuse
Tarraco
Timgad
Tower of Hercules
Trier - best example of several Roman sites within the same city and iconic
Villa Adriana, Tivoli - best example of a "Roman Villa"
Villa Romana del Casale - mosaics depicting everyday life in Ancient Rome
Volubolis

Plus (brought over from different category):
Rome