Standing right beside the Mohammad Al-Amin Mosque, the Greek Orthodox Cathedral of St. George is Beirut's oldest standing church. The current building dates from the 18th century, but it sits on the ruins of a 5th-century basilica.
The crypt-museum below is the highlight. Glass walkways trace the layout of streets, shops, and houses of late-Roman Berytus, all destroyed by the catastrophic 551 earthquake and tsunami that levelled the ancient city. Entry is small fee and the curators are happy to explain. Allow 30 minutes.