Original: There were cities in the vicinities of Beijing by the 1st millennium BC, and the capital of the State of Yan, one of the powers of the Warring States Period (473-221 BC), Ji, was established in present-day Beijing.
Simplified: The center of Beijing was settled in the 1st millennium BC. In those days, the Kingdom of Yan set up their capital where Beijing is today. They called it Ji.