What is define firmament?

The firmament is a traditional concept in ancient cosmology and is defined as the expanse of the sky or heavens. It is considered a solid, domed structure separating the Earth from the celestial realm above. This concept was prevalent in ancient civilizations like the Babylonians, Hebrews, and Greeks and believed to be made up of transparent crystal or hard, metallic substance. The firmament was considered the place where celestial bodies like stars, planets, and the sun and moon were situated and were seen as a divine symbol of God's greatness and power. Today, the concept of the firmament is regarded as a metaphorical and poetic reference to the sky and heavens.