'First born' in the Bible

Then Joshua made them take an oath at that time, saying, “Cursed before the Lord is the man who rises up and rebuilds this city, Jericho; with the loss of his firstborn he shall lay its foundation, and with the loss of his youngest son he shall set up its gates.”

Now this was the lot (allotment) for the tribe of Manasseh, for he was the firstborn of Joseph. To Machir the firstborn of Manasseh, the father of Gilead, were allotted Gilead and Bashan, because he was a man of war.