Trogyllium was a promontory and small city on the Ionian coast opposite the island of Samos, mentioned in some manuscripts of Acts as a stopping point during Paul's third missionary journey. The name appeared in various spellings in ancient sources, reflecting the fluidity of proper name transcription. While some major New Testament manuscripts omit this reference, others preserve it as a geographical detail of Paul's coastal voyage. The location was well-known to ancient mariners as a navigational landmark where ships could anchor in the strait between the mainland and Samos.