Colombo has historically been Sri Lanka's principal port and commercial hub since colonial times. While the question states 'only sea-port', Sri Lanka actually has multiple ports (Trincomalee, Galle, Hambantota), but Colombo remains the largest and most significant. Ambalangoda, Galle (spelled 'Gall' in the question), and Beruwala are coastal towns but Colombo is the major port city and former capital. The question has a factual inaccuracy in claiming it's the 'only' port.