The Zero Age is of some unknown length. If fragmentary records can be trusted, the Serpent Folk arose in the swamps and marshes some thirty-thousand years before 1 IY, and discovered agriculture around 20,000 BE (Before the Empire). They formed squabbling city states, then nations. By 10,000 IY, they ruled the world or at least this part of it, except for the areas where the Koru behemoths chose to walk. They enslaved the other races, but over time grew decadent and weak and allowed their slaves to do more and more.
Then came the Wizard King. He led a slave revolt, himself a trusted slave of a Serpent-Folk sorceror. He invented Wizardry and taught it to others and, allied with the Gods and their priests and the first High Druid and the Elves and Dwarves, he cast down the Serpent King and destroyed them, then created a kingdom he ruled for centuries from the Island of Omen.
But even magic could only last so long; he sought immortality. But undeath brings corruption and now his erstwhile allies rose against him. The Five moved against him and he slew the White and turned him into a Dracolich. The Orc Lord slew the White while the Four were off licking their wounds, and then went on to defeat the Lich King. The Emperor, Elf Queen, and Dwarf King sealed the Lich King away on Necropolis, ideally forever.
Thus ended the Zero Age. Thus history began with the Coronation of the First Emperor in Axis.