Agade was the capital of the king Sargon of Akkad, who ruled the regions of Akkad and Sumer. After the regions of Akkad and Sumer combined into Babylonia, Agade remained a leading city for a long period.
The city Akkad is mentioned in the Old Testament (Gen. x. 10) only once. It has been suggested that Akkad is a name from the Hebrew language. Greek language varients are aroad or achad. In the Old Testament it is described as one of the four chief cities, Akkad, Babel, Erech and Calneh, which constituted the nucleus of the kingdom of Nimrod in the land of Shinar or Babylonia. The name Agade is probably from the Sumerian language, appearing in texts such as the Sumerian king list. The later Assyrian-Babylonian Semitic form Akkadu ("of or belonging to Akkad") is probably derived from Agade.
It is possible that the name Agade may mean "crown (aga) of fire (de)" in allusion to Istar, "the brilliant goddess," the tutelar deity of the morning and evening star and the goddess of war and love, whose cult was observed in very early times in Agade. This is suggested by the writings of Nabonidus, whose record  mentions that the Istar worship of Agade was later superseded by that of the goddess Anunit, another personification of the Istar idea, whose shrine was at Sippar. It is significant in this connexion that there were two cities named Sippar, one under the protection of Shamash, the sun-god, and one under this Anunit, a fact which points strongly to the probable proximity of Sippar and Agade. One theory held (as of 1911) that Agade was situated opposite Sippar on the left bank of the Euphrates, and was probably the oldest part of the city of Sippar.
SUMMARY: The city-state of Agade has never been found. It was the capital of Sargon and is the toponym for the Akkadian Civilization .....