What did Nehemiah lead the people to rebuild?

Answer: The wall of Jerusalem

Nehemiah told the people, "Come, let us rebuild the wall of Jerusalem," and they set their hands to the good work.

“Then I said to them, “You see the trouble we are in. Jerusalem lies in ruins, and its gates have been burned down. Come, let us rebuild the wall of Jerusalem, so that we will no longer be a disgrace.””— Nehemiah 2:17 (BSB)