Sentences of a paragraph are given below in jumbled order. Arrange the sentences in the right order to form a meaningful and coherent paragraph.

A. At its height, around 1,200 years ago, the city of Calakmul had a population of about 50,000 people, but the kingdom as a whole numbered more than 1.5 million.

B. Deep in the jungle of southern Mexico lie the ruins of a city that thrived for centuries before it was abandoned more than 1,000 years ago.

C. Archaeologists have uncovered 6,750 structures here-the largest is this pyramid temple, called, simply, 'Structure 2.'

D. Calakmul was once one of the two duelling superpowers-along with Tikal-of the Classical Mayan civilisation.