 Filming an episode abroad had been suggested in 2004 , but the episode was the first such occasion . Planning began in April 2007 , before Moran had written the script , and continued until the production team travelled to Italy . Several weeks before filming started , a fire disrupted the production . Moving to Rome caused problems for the production team : the equipment truck was delayed for several hours at the Swiss border ; the special effects team were delayed for twenty @-@ four hours at Customs in Calais . The production team only had 48 hours to film on location . The aftermath of the eruption was filmed on the same night as the location shots . To create the falling ash , the special effects team used a large mass of cork , with a " constant supply of debris raining down " . Scenes set at the Temple of Sibyl were filmed at the Temple of Peace , Cardiff on 18 and 19 September 2007 . 
