Explanation:
There is one bygone civilization, which came to my mind, right after having read your question, which is Srivijaya. Srivijaya flourished between the 7th and 13th century CE. It comprised of Sumatra, the western part of Java, and the southern peninsula of Malaya. It was a conglomeration of city states, with centers at Palembang on the island of Sumatra, and ancient Chaya which was nearby the present city of Surat Thani in southern Thailand. This area in particular became rich because of the two different monsoons, the summer monsoon blowing from the southwest, and the winter monsoon blowing from northeast.
