Greece had an oral tradition until the Homeric poems were finally collected and written down (it is highly unlikely a man named Homer wrote everything attributed to him) and these dealt with the gods' stories and what to take away from them. Then a man named Hecataeus, what they called a logopoios, is thought to have traveled the Mediterranean, recording customs, topographical descriptions, and ethnic traditions. Herodotus mentions him four times in his works. Both were very mythological in nature.

What sets Herodotus apart was that he wrote down what we today can recognize as history; the Greeks really didn't care about their actual history; the tales of their gods was enough for them. Herodotus tells us of the rise of Persian power, the friction it caused with the Greeks, and of the famous battles they fought. He does not limit himself to the Persians and Greeks though, including Egypt and Scythia for instance, and incorporates their legends and customs to bring us not just historical material, but sociological observations, skeptical considerations on mythology, political theory, and much more.

To sum up, what he had to work with was oral traditions and stories; he didn't have manuscripts to draw upon. A quote of his, "I record what I have heard, but I do not have to believe it. You may take this as my principle throughout my work."

TL:DR Before Herodotus the past was not that important; anything you needed to know about the world was in your myths. He started the practice of recording what was going on in the world with men instead of gods.

Source The Greek Historians - Norman Austin