The earliest Maya settlements date to around 1800 B.C., or the beginning of what is called the Preclassic or Formative Period. The earliest Maya were agricultural, growing crops such as corn (maize), beans, squash and cassava (manioc). during the middle Preclassic Period, which lasted until about 300 B.C., Maya farmers began to expand their presence both in the highland and lowland regions. The Classic Period, which began around A.D. 250, was the golden age of the Maya Empire. Classic Maya civilization grew to some 40 cities, including Tikal, Uaxactún, Copán, Bonampak, Dos Pilas, Calakmul, Palenque and Río Bec; each city held a population of between 5,000 and 50,000 people. At its peak, the Maya population may have reached 2,000,000.