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.