One of the first things we do each year when we get to Ziyaret Tepe is to relocate our survey points on the site and to re-establish our “site grid”. An important thing to know about most archaeologists: we have obsessive interests in recording the precise location of all the ancient walls, pits, hearths, floors, and artifacts we find on our sites. In order to do this, we create detailed gridding systems which allow us to record the location of ancient features and artifacts in three dimensions. Conceptually, our site grid is a projection of north-south and east-west, lines that divide Ziyaret Tepe into 10m by 10m squares, to which we add a height above sea level.
In 1997, on the very first morning of work at the site, I drove a 1.5m long piece of iron rebar into the citadel mound at an arbitrary (and convenient) point and assigned this precise spot the coordinates N1000 E1000, meaning that it was 1000m north and 1000m east of an point well off site (called an “imaginary datum”). From an old Turkish state map, I determined the elevation at that point was 568.09m above sea level. All spatial measurements made subsequently over the past 15 years reference this initial survey point.
So, our typical excavation unit is a 10m by 10m grid square with each corner located at the intersection of two lines in our site grid. For example, N980 E1170 is the grid point 20m south and 170m east of that piece of iron rebar. We then record the precise location of important features or artifacts within these grid squares, again relative to the iron rebar. I can tell you, for example, that artifact ZT 29303 (an iron pin) was found at N989.28 E1173.63 elevation 568.38m (9.28m north and 3.63m east of the grid corner). I could, if I wanted, put the iron pin back in its original findspot within grid square N980 E1170.
I told you we were a bit obsessive.
Why do we do this? Part of the analysis of archaeological sites involves studying the spatial relationships between different artifacts, and between artifacts and their surrounding features. This detailed level of recording is necessary to allow us to reconstruct the site, either on paper or, increasingly, through CAD and other computer assisted modeling.
A few days ago, Chelsea and I went out and, using our total station and my notes from 1997, we relocated that same piece of iron rebar, still firmly in place at N1000 E1000, we established the north-south line, and started laying out survey and excavation points for this year’s work.
I’ll tell you about our first few days of survey in a subsequent post.
