One strand of evidence allowing scholars to date ancient Mesopotamian kings is provided by the so-called Venus Tablets.

The 9-inch-high fragment at right was excavated at the Assyrian site of Nineveh in 1850 by the British explorer Austen Henry Layard. Although the tablet dates to the seventh century B.C., its cuneiform text refers to the Old Babylonian king Ammisaduqa (1646–1626 B.C.), who reigned about a century after Hammurabi (1792–1750 B.C.). Thus scholars believe that the Nineveh tablet—along with several other identical tablets that have also been found—is a copy of a tablet originally produced a thousand years earlier.

These tablets are called the Venus Tablets because they record observations of the risings and settings of the planet Venus (as both morning and …