Decanus Vulso is an Imperial guard for the Temple of Mara. The Temple was attacked by bandits and the guards tracked them back to the ruins of Fort Sphinxmoth. The guards were outmatched and captured Decanus and his fellow guards, Eliana Salvius and Veranus Macatus. The Priestess of the Temple, Rafora Casca, is near the ruins looking for help to retrieve the items stolen by the bandits.
After you aid the quest, he'll say: "I thanked you for saving me from the crocs, and now I can thank you for saving our holy relics. Mara bless you, my friend."