Producers agreed that it should rain for the duration of the episode. (Stopping only with the arrival of Sura.) Most of the rain that is seen, is digitally added;the actors were sprayed with water to aid in the illusion that it was actually raining.
The character Aulus is introduced when Sura arrives at the Ludus. Portrayed by Mark Mitchinson, he along with Craig Parker (who portrays Glaber) and Tania Nolan (who portrays Caecillia in later episodes) each had minor roles in the film "Underworld: Rise of the Lycans."