In 1935, when Mary-Helen Schmidt presented her husband, Professor Erich F. Schmidt, then field director of the Persepolis, Rayy, and Luristan expeditions, with an airplane for the purpose of aerial survey, she could not have made a more important and valuable contribution to archaeology. There had been pioneer work in aerial photography in the past,5 but this was the first time that a thorough and well-planned aerial survey exploration was to be undertaken on such a large scale.

It was not until 7 August, 1935, when permission was finally granted, that the Aerial Survey Expedition under the directorship of Erich Schmidt could begin its work. Commenting on the many months of waiting and preparation, Schmidt writes: “There is no need to speak of our personal feelings, then and afterwards. Enough to say that happy satisfaction of accomplishment accompanied the immeasurable broadening of the scope of our work.”6

The airplane, christened Friend of Iran, was flown by Lewin B. Barringer in 1935-36 and William G. Benn in 1937. Frederick Lillich was its mechanic and technical assistant. The photography was done by Erich Schmidt and his assistant Boris Dubensky.

The aerial photographic operations were divided into three parts: (1) flights over excavations already in progress, such as Persepolis and Rayy; (2) aerial documentation and mapping of sites under consideration; and (3) reconnaissance and exploration flights over archaeologically unknown areas of Iran.

Aerial photographs of work in progress not only gave an overall view of the extent and layout of the excavations but also often sped up ground operations. Documentation and mapping helped to lay the groundwork for and to pinpoint areas where digging could begin, while the reconnaissance flights facilitated the mapping of ancient sites, mounds, or fortresses that had been mentioned in ancient writings but had never been explored. These aerial survey photographs, especially those of structures above ground at an excavation in progress, could be used to achieve positive results only when coordinated with the plans of the field architect.

Before the Friend of Iran could start its photographic flights over sites being excavated, mapped, or documented, the ground had to be prepared in such a way that the aerial photographs could be easily applicable tc the ongoing excavations or to selecting new ones. Base points were marked on the ground, using quadrants of 100-meter squares subdivided into excavation plots of 10 x 10 meters. To make them more easily recognizable from the air, these base points were marked by white cloth circles, two to three meters in diameter, with black centers. With an aerial photograph in hand clearly showing the base points, one could draw white lines on the photographs to connect corresponding points. The result would be a grid of squares from which the excavator could determine quickly and accurately where to start digging.

In addition to these ground preparations, additional means had to be employed to achieve the most accurate results through aerial survey. Photographs had to be taken at different hours of the day, under different weather conditions, and during different seasons. The seasonal changes in the ground cover were utilized to obtain the most versatile and conclusive photographic results. An excellent example, showing the contrasting as well as complementary results, is provided by two photographs of the Mound of Istakhr taken in two different seasons. The autumn photograph (llA8) records the relief of the fortification wall and its round towers but shows only very faint depressions of streets. In the spring photograph (l l A9), the streets stand out as very distinct white lines. This is the result of a less dense ground cover over hard-tramped areas, buried walls, and foundations. These and many other details are not visible on the autumn photograph.

Another important way to detect structures covered for centuries by sand was to photograph the area in question during the first two hours after sunrise. Then the slanting rays of the sun would highlight the slightest elevations, which would be invisible to the surveyor on the ground. In order to gain a good understanding of the topography of a site, vertical and oblique photographs were also necessary. For excavations in progress, oblique views were much more useful, for they showed certain proportions of heights of buildings or remnants of walls far more clearly. Vertical views were more valuable for the general mapping of an area, where certain formations and discolorations were visible only on an aerial photograph.

In just two short seasons, Erich Schmidt and his crew made numerous survey flights and took hundreds of aerial photographs. In the season of 1935/36, Persepolis and environs in southern Iran, including the Islamic city of Istakhr, the sacred precinct of Naqsh-i-Rustam, the prehistoric mounds of Tall-i-Bakun, Rayy near Teheran in the north, and sites in the valley of Rumishgan in the western mountains were photographed. Flights of the 1937 season concentrated on northeastern Iran — the Gurgan plain and the ancient defense wall, often erroneously called “Alexander’s Barrier,” which stretches from the Caspian Sea to the mountains in the east. Other flights of that season were made to northwestern Iran, including Azerbaijan, Tabriz, and Mount Ararat, and to Luristan in westcentral Iran.

Finally, during the 1937 season exploratory flights were undertaken for the purpose of tracing and pictorially documenting many sites in the environs of Persepolis and of establishing their locations on archaeological maps for use by future excavators. About this, Erich Schmidt wrote: “In thirteen hours of flying over the environs of Persepolis we succeeded in mapping more than four hundred ancient sites in the plain of Persepolis. A task of years if carried out on the ground.”7

Aerial photography, a fairly new branch of archaeology, proved to be a unique tool for showing ancient sites in their topographical environment. It thus enables the archaeologist, in a very short time, to identify a site and, consequently, to assign the exact location of a forthcoming excavation.