By the time Sarah was seventy-six years old, she felt certain she would never give Abraham a child. “Go and sleep with my servant,” she told him. “Perhaps I can have children through her” (Genesis 16:2). Abraham slept with Hagar, and Ishmael was born.

This was a perfectly respectable practice for infertile couples in the ancient Middle East. Similar laws and references show up in many ancient documents form the region where Abraham was born and raised in what is now Iraq: an early Assyrian marriage contract (1800s BC), the Code of Hammurabi, king of Babylon in what is now Iraq (1700s BC), and Nuzi stone tablets from northern Iraq (about 1500 BC).

This is an excerpt of a marriage contract from the Nuzi tablets: “If Giliminu [bride’s name] will not bear children, Giliminu will take a woman of Lullu-land [apparently famed for excellent slaves] for Shennima [groom’s name].”

Law 146 from Hammurabi states: “If a man marries, and his wife give him her servant to bear children, and then this servant starts acting like she’s equal to the wife because of this, the wife isn’t allowed to sell her. But she can put a slave mark on her and treat her as a slave.