In Tolkien's early writings, the eagles were distinguished from other birds: Eä, the World, was bounded by the Walls of Night, and the space above the Earth up to the Walls was divided into three regions; common birds could keep aloft only within the lower layer, while the Eagles of Manwë could fly "beyond the lights of heaven to the edge of darkness". The conception of the limited world and of the layers of the firmament was rejected during the writing of "The Lord of the Rings".