The discovery of Troy’s ditch, cut around the lower city’s perimeter to thwart the hard-driving enemy chariots, was first made without a single stroke from a spade. Today’s archaeologists need not rely only on experience and intuition in deciding where to dig. They also employ technologies that allow them to “peer” beneath the ground and measure changes in the composition of the soil.

Using an electronic apparatus that measures electrical resistance in the ground, physicist Hans Günter Jansen has charted large areas of the Roman lower city. This piece of equipment, however, can only measure changes in soil composition to a depth of around 3 feet. So in 1992, the scientists began using a cesium magnetometer, a far more sensitive instrument, to probe deeper beneath Troy’s surface. This device—the only one in the world currently available for archaeological purposes—detects disturbances in the earth’s magnetic field to a depth of 10 feet below the surface. The resulting data are processed and graphically displayed by a computer. It was with the cesium magnetometer that scientists discovered and tracked the ditch.

But such modern technologies cannot entirely replace picks and shovels. The data, for example, do not reveal the ages of structures that are found beneath the surface. And a trench from World War I (of which there are plenty in Troy) does not show up on the computer graphics any differently from a Bronze Age ditch. Similarly, scientists cannot distinguish on screen between an elevated structure, such as a wall, and a depression, such as a ditch. Measurements from the magnetometer and other advanced technologies cannot replace excavations, but they do indicate where the digging should take place.