Complexities of Strata
Unfortunately, unlike a layer cake, a stratum of a tell will not be uniform in thickness or comprehensive in covering the site for several reasons. Some sections may erode faster than others making the stratum uneven. Also, the movement of water can move small (but datable) materials away from their original setting. Ancient peoples may have used one area more than another; thus, causing strata to accumulate at different rates. Some parts of a tell may go unoccupied while people live on other parts. This will create strata that only partially cover the tell.
There are other complexities we must consider. Down grading, fills, pits, and foundational trenches alter or destroy stratigraphy.
Grading Down
Just as people today need level places to build a home, ancient people needed level places too. There are two ways to level an area: grade down or fill up. Both of these methods alter the natural development of stratigraphy. Grading down is removing soil and debris from an area. Removing soil and debris from its original context removes a piece of the history of the site and creates an artificial stratigraphy, that is, two layers that are incongruent in sequence and time. The archaeologist can usually recognize graded down areas only by comparing this stratigraphy with other stratigraphic sections on the tell.
Fills
A fill may seem harmless since the soil is brought in from another location in order to raise an area. However, just imagine what happens if the soil used for the fill is removed from one place on the site (where people had lived) and is relocated to another place. Let’s say an Iron II Age person dug soil from an Early Bronze Age level that was exposed at another place on the site and placed this soil (with datable debris) on top of a Late Bronze level and then built an Iron II Age house on it. The archaeologist would find the Iron II house on top of Early Bronze debris, which is on top of Late Bronze debris. Of course, the problem is that the Late Bronze material should be on top of the Early Bronze material if the stratification is natural, not the other way around. (I haven’t mentioned the problem the archaeologist will have when he/she tries to determine the stratigraphy where the Early Bronze material was removed.) Now the archaeologist has the task of determining why the strata are out of chronological order.
Pits
Another occupational feature destructive to stratigraphy is pits. Defined simply, pits are holes dug into the ground. {Photo 1981 near here.} These holes, when initially dug, destroy earlier stratigraphic layers and create new ones. People dug pits for many reasons. Pits functioned as storage bins, grain silos, trash dumps, latrines, cisterns, tombs, etc.
Archaeologists treat a pit as a separate stratum, with the material in the pit used to help date when the pit was in use.
Some people dug pits looking for previously used building materials. If building materials are reused, this creates an additional problem: styles from one period being used in walls of another period. Not only does the digging destroy stratigraphy, but also the reuse of materials can confuse the dating of structures.
Pits can have natural causes. Roots from trees growing on the site can create pits through their growth and decay. Yet tree roots are generally small and are easily recognized. The more destructive natural cause for a pit is a rodent hole. Rodents make larger holes than tree roots and rodents tend to carry foreign material into their holes for their nests. While excavating at Tell Halif in Israel, I saw where a modern rodent had dug a hole down to the Iron II strata and created a nest there. Inside this nest we found plastic, a very modern material!! Fortunately, we had been careful in our excavation and had recognized the rodent’s intrusion before we found the plastic.
Foundation Trench
A foundation trench is another element destructive to stratigraphy. As one would build a home today, ancient people dug trenches to lay a foundation for a new building. Foundation trenches disrupt stratigraphy, like pits, in that they intrude and destroy previous levels of occupation and introduce a new one. However, the material found in a trench next to a wall can help date the wall itself.
Modern Occupation
Ancient tells are not immune from modern settlement. Some modern villages settle around tells, such as at Tell Heshban. Other villages actually cover the top of ancient tells, such as the modern town of Madaba in Jordan. These modern villages continue the development of the tell. Unfortunately, many modern building practices disrupt and/or destroy earlier strata of the tell.