Cairo is Egypt's capital and the largest metropolis in Africa, which today has a population of almost 18 million, has its origins in the city of On on the east bank of the Nile, later called Heliopolis by the Greeks, and in Mennofer, the Greek Memphis, on the west bank. The site was chosen in 3100 B.C. by King Menes, first king of the 1st Dynasty, for his capital. From here, he could control the newly united Upper and Lower Egypt.