What is a Tell?
Many of the oldest cities in the world are called tells (also spelled tel, til or tal). The word 'tell' is from the Arabic language, meaning mound or mount. Ancient cities, like modern ones, experience natural and cultural disasters, such as fires, earthquakes, and assaults from enemies. If a city's structures were demolished in prehistory, there was no way to remove all the demolition rubble; people built right on top of the ruins.
In many ancient cities, such as the site of Hisarlik thought to be ancient Troy and shown in the figure, there are many many layers of old building debris, as citizens rebuilt again and again in the same locations. Archaeologists call the layers in an archaeological site the 'stratigraphy'.
Modern cities today are also tells, although no-one calls them that. Beneath the streets of most modern cities have been found cemeteries, streets, and building foundations from centuries ago. For example, in New York City recently was discovered the 19th century streets and building foundations of the notorious Five Points neighborhood several feet below the modern city streets. The medieval remains of a hospital were discovered six feet below the modern surface of Spitalfields in London.
Because of the complex stratigraphy found by archaeologists in modern cities, a special branch of archaeology has developed called urban archaeology, with its own set of tools and processes.
Buried cities, whether modern or ancient, develop extremely complex stratigraphy as buildings fall and are rebuilt. One very useful tool archaeologists use to keep track of the levels in an urban or tell situation is called a Harris Matrix.