I am currently in a rather unusual 3000 BC Spain game. The world was strange when I spawned, and has only gotten stranger since.
Greece still exists! And the Byzantines never spawned; in fact the Romans never even conquered Byzantion. The Romans are gone, too. Yet, they did manage to conquer Greece: Athens and Sparta both have a Roman Road in their main tile. France also shows clear signs it used to be a Roman province. My guess is that the Romans collapsed soon after conquering Greece, allowing Greece to retake their old cities (maybe from Byzantion before it declared independence?).
Unlike Greece, China is gone.
Now we get to the really strange part: Greece is not the only unusually long-lived civ: Persia and India are both absolute powerhouses. In fact, Persia is so strong they had retaken Jerusalem and Babylon from the Arabs by my spawn, and a few turns later India of all people took Mekka from them. The Arabs survived in Egypt, though...
Even after the Egyptian respawn made a royal mess of things.
The Greeks eventually collapsed. But the Persians just kept on going and took Byzantion and began to push into crazily divided Egypt, attacking both civs there. Then, the Seljuks began to spawn, and I was sure it was the end of the Persians. I have never seen AI stand up to the Seljuks...
Until this game. The Persians completely slaughtered the Seljuks; only Babilon and Pura fell to them, but those were reconquered within the turn. Unfortunately I didn't screencap before the Byzantine respawn (well, first-time spawn, really) cost them Byzantion. Right now I'm wondering whether they'll be able to handle the Turkish spawn as well as the Seljuks. I should also add that the Persians are still Zoroastrian, and have in fact managed to make their religion the third-biggest of the world (after Catholicism and Buddhism).