The ten plagues God sent to Egypt through Moses and Aaron were meant to persuade Pharaoh to let the Israelites go free from slavery. Each plague increased in severity, from turning the Nile river to blood and bringing frogs, to pestilences of lice, flies, livestock disease, boils, hail, locusts, darkness, and finally killing all firstborn sons of Egyptians. Despite the plagues, Pharaoh's heart was hardened and he refused to release the Israelites until the death of his own firstborn son. Only then did he let the Israelites flee Egypt, but pursued them until being drowned in the Red Sea.