Ancient Ephesus was a great trading city and a centre for the cult of Cybele, the Anatolian fertility goddess. Under the influence of the Ionians, Cybele became Artemis, the virgin goddess of the hunt and the moon, and a fabulous temple was built in her honour. When the Romans took over, Artemis became Diana and Ephesus became the Roman provincial capital.
Of Turkey's hundreds of ancient cities and classical ruins, Ephesus is the grandest and best preserved. Indeed, it's the spunkiest classical city on the Mediterranean and the ideal place to get a feel for what life was like in Roman times.
In 356 BC the Temple of Cybele/Artemis was destroyed in a fire set by Herostratus, who claimed to have done it to get his 15 minutes of fame, proving that modern society has no monopoly on a perverted sense of celebrity. The Ephesians planned a grand new temple which, when finished, was recognised as one of the Seven Wonders of the World.
To avoid the heat of the day, come early in the morning or in the late afternoon, when it's less crowded. If you can, avoid public holidays altogether. Bring water with you as drinks at the site are expensive.