It has been made for the 150th anniversary of the Munich Patek Philippe retailer in 2006, as mentionned in 25 ex. in RG (there is also a WG version, I don't know if other gold/Pt colors were used as well).
It looks fabulous and I must say I still like Roman numerals a lot and would like to see more of them in the current collection.
Thanks a lot for sharing Patrick 
Cheers, Mark