Metropolitan cities or major city that is the capital of the ancient Khmer came hundreds of years and the "Angkor Thom" will not mean the castle is the only Castle in Angkor Wat.
Or imply that the capital city was the capital of the Khmer Empire for hundreds of years and the "Angkor Thom" shall mean the castle, the castle just as Angkor Wat.
Or the Royal Angkor means big city is the capital of the ancient Khmer for hundreds of years, and "Thom" means not only the castle castle once Angkor Wat.