To date, historians believe that one of the earliest mathematical writings came from the Babylonians—a clay tablet “written” around 2000 B.C.E. (although some researchers approximate the date at 1800 to 1600 B.C.E.). This clay chunk showed an image that looks like a square with two diagonal lines slicing the square equally—like an X in a square. In reality, it represents a sexagesimal numerical approximation of the square root of two—the length of the diagonal in a unit square. This was no doubt needed in the construction of ancient buildings and monuments, as being able to compute the sides of a triangle—not to mention square roots—was very necessary.