Two were situated in the dense jungle of Africa, while the other two were set in the remote areas of the Arctic. One was the refuge for a Scarlet Speedster, the other the sanctuary of a Winged Warrior, while these city's metropolitan dopplegangers were only briefly seen by a few.
Remarkably, on Earths One and Two there were intelligent civilizations of both gorillas and birds. There were other such secret civilizations on both Earths such as the twin underwater cities of Atlantis, the hidden lands known as Paradise Island, and the miniaturized city of Kandor. Yet known house intelligent non humanoid inhabitants like these four fabled fort..
Most forget of the subterranean Bird-People whom Grodd encountered underneath Earth-One or the Gorillas whom Zatara met in the central plains of Africa. Yet most remember Earth-One's Gorilla City and Earth-Two's Feithera. Gorilla City, led by King Solovar, was the metropolis of gorillas... Feithera, led by King Worla, the metropolis of bird-people.
The Earth-Two version of Gorilla City was left extinct after Zatara dealt with its residents by immobilizing them. The Earth-One version of Feithera remained secluded, separated from the prying eyes of humanity save for its two temporary visitors in Grodd and Flash.