Factual error: When Van Helsing goes to Rome, the subtitle refers to the Vatican as "Vatican City". By the 1880's the Pope had lost all his temporal power, and his previous lands (The Papal States) were taken by the new Italy. The Vatican had no lands or authority over any of Italy or Rome. The Pope was a virtual prisoner inside the Vatican. Only with the Lateran treaty in 1929 (with Mussolini) did the Vatican gain independence as the "State of Vatican City".
Factual error: In the beginning of the scene after Van Helsing kills off one of the three female vampires, there is a map behind Friar Carl depicting the whole of the Carpathian basin, which, at the time, included the Austro-Hungarian empire as well as a part of Romania. However, the whole area is labeled "Transylvania", which is only a region of Romania.
Factual error: On the map, Budapest is indicated to be just as large as Transylvania, or at least of the same size category. Apart from Budapest being only a city and Transylvania a pretty large county, Budapest (taking its 19th century size) is not more than 500 square kilometres while the Transylvanian region is circa 57000 square kilometres.