Seventy seems to be a pivotal number in the Jewish story.
Seventy is the minimum number of people who can represent Israel, there were seventy elders of the people. There are seventy interpretations to the Torah. 70 letters in the ineffable name of Hashem. Significantly, Yocheved, mother of Miriam Aharon and Moshe, was born in between the walls of the city as they arrived. Yocheved was the last of the 70.