Which was the first building built entirely in marble?

The first building constructed entirely of marble is generally considered to be the Temple of Artemis at Ephesus, one of the Seven Wonders of the Ancient World. Completed around 550 BCE, it was renowned for its grandeur and elaborate sculptures. The temple was dedicated to the goddess Artemis and showcased the use of marble not just as a structural material but also for artistic expression. Its architectural significance influenced many subsequent structures in the ancient world.