Which ancient Greek city-state hosted the Isthmian Games?

Corinth hosted the Isthmian Games at the sanctuary of Poseidon on the Isthmus of Corinth.

The Isthmian Games were one of the four major Panhellenic festivals of ancient Greece, alongside the Olympic, Pythian, and Nemean Games. They were held in honor of Poseidon at a strategically important site near Corinth, where routes between mainland Greece and the Peloponnese converged. Corinth controlled and organized the festival for much of its history.

The games included athletic events such as wrestling, boxing, horse racing, and the pankration, as well as musical and poetic contests. They were held in the second and fourth years of each Olympiad, meaning they took place both before and after each Olympic Games. A common mix-up is to answer Athens because Athenians were especially prominent participants and received privileged seating; however, the host city-state and administering power was Corinth.