Originally, Isis' cheaper technology bonus also applied to Age advancement (for example, advancing to the Classical Age only costs 360 food rather than 400). As of The Titans patch 1.02, that is no longer the case.
The daughter of the earth god Geb and the sky goddess Nut, Isis became the mother goddess of Egypt. When Osiris, her brother and husband, inherited the rule of Egypt, she worked together with him to bring civilization to the Nile Valley. She taught cloth making and curing the sick, and introduced the concept of marriage. She ruled Egypt wisely while Osiris traveled the world spreading civilization elsewhere. Isis was able to resurrect Osiris after he had been killed and dismembered by Set. She assisted at Osiris’ embalming in preparation for his journey to his new kingdom in the land of the dead, thereby helping to create the Egyptian rituals of burial. She secreted her son by Osiris, Horus, until he was able to seek revenge in a long contest that eventually saw the end of Set. The magic of Isis was a very powerful aid in attaining a favorable judgment from Osiris. Her magic abilities improved greatly when she took advantage of Ra’s agedness to trick him into revealing his name, giving her access to some of his power. She is often portrayed suckling the child Horus.