This is where they hold tournament of all kinds. They also hold tournament in honor of Nagi at times. Negi and Kotaro have fought here under disguises and the names Nagi and Kojiro. They fought to free Negi's three enslaved students, 1 million Drachma (or was it 100 million, or 1 billion...? im not looking at my book to verify that >w<). Tournaments and betting on fights are a very popular thing to do in Ostia, stop by and watch or sign up and fight!