Argo City, Krypton was one of three principal city-states located on the continent of Lurvan on the planet Krypton (the other two were Kandor and Kryptonopolis).
In Supergirl, the surviving members of the Kryptonian race were saved by Zor-El when he created a force field around Argo City, also saving his wife but losing his life in the process. Had the force field worked Alura would never send her daughter into space in the first place.
Argo City also inspired the creation of Krypton's sister planet from the DC Animated Universe