The 59-foot-tall Akapana resembles a large natural hill more than a pyramid. Closer inspection shows walls and columns sticking out from the base and carved stones on its summit and tumbling down the sides. The somewhat amorphous shape of this tremendous pyramid is the result of centuries of looting and quarrying of its stones for colonial churches and even for a railway built in the 1900s. New research shows that this pyramid was never quite finished in antiquity.

At Tiwanaku we seem to have an interesting situation where the city's previous infrastructure was razed and completely redone just before the city was suddenly abandoned. It seems that around A.D. 700, three centuries into the existence of Tiwanaku as a monumental and powerful city, there was a sudden change to direct all construction efforts toward building what was the largest structure in the Andes. The previous monuments of the city were torn down and their stones reused to build the Akapana pyramid. The effort was too great, and the pyramid lay unfinished when the city was abandoned. One Spanish chronicler said of Tiwanaku, "They build their monuments as if their intent was never to finished them."

Around the rising pyramid, the arrangement of small single homes was replaced by large square compounds--also using the scavenged remains of previous monuments--serving perhaps as ritual places for powerful families or ethnic groups. What this change represents is unknown at the present. We could be seeing the rise of a powerful king, a popular religious movement, or the formation of a multicultural city. Whatever the cause behind this massive transformation, it didn't last long. By A.D. 950 all monumental construction suddenly ends with stones in various stages of dressing scattered around the partially built monuments.

One of our project's aims is to uncover Tiwanaku's form before its sudden demise. Because the Akapana pyramid and the area around it is too large to excavate in a single season, or even for a single project to undertake, we will use ground-penetrating radar combined with small selective excavations instead of traditional methods. We plan to survey the area around the pyramid to a depth of several meters and excavate based on the subsurface images generated by the equipment (recently donated by the government of Japan). Using a variety of computer programs, we'll be constructing a three-dimensional model of the city both above and below ground (see map for areas of investigation).

Click here for a 360° view of the
top of the Akapana pyramid (QuickTime; 600k).

June 29, 2002
Update by Kimberly Henderson

Our research involves the use of ground-penetrating radar to detect subsurface architecture surrounding the Akapana pyramid. This method of subsurface prospecting entails the transmission of high-frequency electromagnetic radar pulses into the ground from one antenna and the reception of reflections of those pulses off of buried discontinuities with a second antenna at the surface. The goal of this project is to determine, with minimal excavation, the spatial distribution and organization of the architecture that is thought to surround the Akapana pyramid.

The field season began with three surveys in different areas using the 400Mhz and the 200Mhz antennas in order to accurately assess the soil context and its relationship to the radar signal in terms of velocity and depth. The soil has a high percentage of clay, which seems to be slowing down the radar signal quite a bit, making prospection difficult since the architecture is located at varying depths below the surface.

We are currently processing the preliminary data from these surveys as carefully as possible so that the actual depth of the subsurface architecture can be calculated. The plan, at this point, is to determine the actual velocity of the radar signal through the soil, convert that value to depth and then decide when and where to use what type of antenna. Once this has been done, we will proceed with several 40x40 meter survey grids that will cover an area of about 100,000 square meters.