There is an interesting temple in central vietnam called the Thap Duong Long ( Elephant tusk) castle built by joint Khmer-Cham people but under the supervision of King Suryavarman 2 during when the Khmers control Champa land. Nearby, the Khmers engineered the first biggest deep water port in all of South East Asian history. This massive port shifted all sea trades and routes from Malacca straits and China to dock at the Cham-Khmer port which boosted the power and wealth of Angkor even further. There are ancient roads from Angkor that connects all these cities and castles together.