Part B How do archaeologists know where to find what they are looking for when there is nothing visible on the surface of the ground?

Typically, they survey and sample (make test excavations on) large areas of terrain to determine where excavation will yield useful information.

Surveys and test samples have also become important for understanding the larger landscapes that contain archaeological sites.

Some archaeological sites have always been easily observable —for example,the Parthenon in Athens,Greece; the pyramids of Giza in Egypt;and the megaliths of Stonehenge in southern England.

But these sites are exceptions to the norm.

Most archaeological sites have been located by means of careful searching, while many others have been discovered by accident.

Olduvai Gorge,an early hominid site in Tanzania, was found by a butterfly hunter who literally fell into its deep valley in 1911.

Thousands of Aztec artifacts came to light during the digging of the Mexico City subway in the 1970s.

Most archaeological sites,however, are discovered by archaeologists who have set out to look for them.

Such searches can take years.