The grounds close to Vipava were the stage of the 384 DC Battle of the Frigidus in which the army of East Roman emperor Theodosius won over the army of Western Roman ruler Eugenius. After this battle, Theodosius for the last time in the history became ruler of united Roman Empire and brought Catholic religion to the West. A detailed description of the battle can be found on Wikipedia. A brief Slovenian version is alo available.