 There are thousands of ancient structures at <unk> and only a fraction of these have been excavated , after decades of archaeological work . The most prominent surviving buildings include six very large pyramids , labelled Temples I - VI , each of which support a temple structure on their <unk> . Some of these pyramids are over 60 metres ( 200 feet ) high . They were numbered <unk> during the early survey of the site . It is estimated that each of these major temples could have been built in as little as two years . 
