The Pergamon Altar was built in the second century BC, in an independent Greek-ruled regional kingdom.
The people of Pergamon spoke Greek, worshipped Greek gods (like Zeus and Athena), and shared the Greek language and culture.
This region, Asian Minor, became part of the Ottoman Empire in early 14th century.
In 1923, the Republic of Turkey formed and replaced part of the Ottoman Empire. Ottoman Empire became many different countries.
In the late 1990s, Turkey first demanded the repartriation of the Pergamon Altar.