Because excavation destroys what it uncovers, modern archaeologists try to learn as much as possible before, or instead of, digging. That work is called survey.
Key idea
Archaeologists find and map sites by field survey (walking the ground and recording what lies on the surface), aerial and satellite images, and geophysics (instruments that sense buried walls and pits). Much can be learned without a shovel, and digging can then be aimed where it will answer a question.
Why it works
Buried things change the ground above them. A mud-brick wall holds water differently from the sand around it, so crops grow differently over it and it shows as a line in an air photograph. Burnt material and fired brick have a different magnetism from the soil, so a magnetometer picks them up. Hard foundations reflect radar waves. Each method measures a contrast, and a contrast in the right shape is a wall, a street or a pit.
| Method | What it senses | Good for |
|---|---|---|
| Field walking | pottery, flint and stone on the surface | finding sites and dating them roughly by surface pottery |
| Aerial photographs | marks in crops, soil and shadows | outlines of walls and ditches over large areas |
| Satellite images | the same, from space, often repeated over years | mapping whole regions; spotting new looting pits |
| Magnetometry | small changes in the earth's magnetism | mud-brick walls, hearths, kilns, filled pits |
| Ground-penetrating radar | echoes of radar pulses from buried layers | walls, voids and floors, with depth |
| Electrical resistivity | how easily current passes through the ground | stone walls and damp ditches |
Worked example: Choosing a method
You suspect a buried mud-brick enclosure under a cultivated field. You may not dig. Which method would you try first?
- Mud brick in damp ground often shows a magnetic contrast with the surrounding silt.
- A magnetometer survey can map a large area quickly without touching the ground.
- The plan it produces shows where, if anywhere, a small trench would answer the question.
Answer: Magnetometry.
Worked example: Pictures from the Cold War
American spy satellites of the 1960s and early 1970s (the Corona program) took photographs that were released to the public in 1995. Why are they useful to archaeologists in Egypt?
- They show the landscape before decades of new building, farming and dam lakes.
- Sites that have since been built over or flooded can still be seen and mapped on them.
- Comparing them with recent images shows what has been lost, and where looting has happened.
Answer: They record sites as they were before modern change.
Common mistake
Thinking archaeology always means digging. Much is learned without a shovel. Survey finds sites, maps them and shows where a small excavation would answer a question, so that less of the site has to be destroyed.
After 2011, repeated satellite images were used to map looting pits at many Egyptian sites, a sad but useful example of what survey from space can show.