When a team begins to dig on a site, the archaeologists first lay out ten meter squares, laying a grid over the entire area they will excavate. Each square is labelled, usually with coordinate points that tell the distance north, south, east, or west of a predetermined starting point.
Four sides of a square each ten meters long are measured. Stakes are hammered into the ground at the corners and string is tied to mark the sides of the square. But having four sides of equal lengths doesn't always make a square. A square must also have four right angles. Archaeologists can check if each square has right angles by measuring their diagonals.
In the illustration, the square with a diagonal line drawn through it looks like two triangles. We know that each of these triangles should have one right angle that is a corner of the square and two sides of equal length. The length of the diagonal should follow the pattern for finding the hypotenuse of a right triangle:
When the archaeologists find that the diagonal measures 14.1421 meters, they know their square really is square. Having squares helps keep track of where things are found. For instance, the archaeologists can mark a bag or bucket with the date the level and the square. All of the sherds of pottery that come out of the square are put into the same container. When they are sorted at the end of the day the excavators still know where and how far down they were found. Also, when a site is mapped by hand, the squares make it easier to create and understand a drawing. The square can be divided into a grid and what is seen in the square is drawn onto a piece of graph paper, matching squares marked on the ground with a corresponding one on the graph paper.
