The Age of Reason
Long before the Tessarid invasion, there lived ancient civilizations not that much different from those that exist today. While those ancient civilizations of Elves, Dwarves, Men and Vaer were not nearly as advanced technologically, it is pretty well accepted by the few scholars who study that time period that the races of Drathl were all the same.
During the Tessarid invasion many fled to other lands, eventually returning once the Reckoning had been completed.
Fourth, Ish, Hamil, Desya, and Lorentzian were all built upon the ruined foundations of pre-tessarid cities. Annas was still completely intact during the entire Tessarid period, and Liesu and Rhienne (the ruined elven city in Greenwood) were both built on the remains of the pre-tessarid elven cities.