As the world’s major trading route, the Mediterranean holds a vast record of history within its depths. Join Bob Hohlfelder, professor emeritus of history, for a fascinating discussion about underwater archaeology. With over 50 underwater archeological expeditions throughout 13 Mediterranean countries, Hohlfelder is an expert specializing in Roman harbors and shipwrecks. Ocean First Divers, 3015 Bluff St., Boulder, will host the event on Thursday, Aug. 21 at 6:30 p.m. Free and open to the public.