The Mekhilta, the tannaitic midrash on Exodus, records a debate among three sages about the size of the "great multitude" (erev rav) that accompanied the Israelites out of Egypt. The verse says simply: "And also a great multitude went up with them, and flocks and herds" (Exodus 12:38). The Torah does not give a number. The rabbis supply three.
Rabbi Yishmael says the multitude numbered one hundred and twenty ten-thousands — that is, 1,200,000 people. Rabbi Akiva doubles the estimate to two hundred and forty ten-thousands — 2,400,000. Rabbi Nathan goes further still: three hundred and sixty ten-thousands — 3,600,000.
To grasp the scale, consider that the Torah counts 600,000 adult Israelite males at the Exodus (Exodus 12:37). Even by the most conservative rabbinic estimate, the mixed multitude that tagged along was twice the size of the Israelite male population. By Rabbi Nathan's reckoning, the non-Israelite crowd was six times larger.
These numbers raise enormous questions. Who were these people? The erev rav included Egyptians, slaves of other nationalities, and various peoples who saw the plagues and decided to leave with Israel. They witnessed God's power and chose to follow. The Mekhilta's escalating numbers suggest that the Exodus was not a private Israelite affair. It was a mass movement that swept up millions of non-Israelites — people who voted with their feet, leaving everything behind to follow a God whose power they had seen with their own eyes.