Unlike every other high civilisation of the ancient world, the Incas did not develop a system of writing based on graphic signs on twodimensional surfaces. Rather, Inca administrative records took the form of three-dimensional knotted-cords made of spun and plied fibers. It is widely believed that khipu technology associated with the rise and expansion of the Inca Empire, during the Late Horizon period (ca. 1400-1532 AD), developed out of an earlier cord recording technology associated with the Wari culture of the Middle Horizon period (ca. 600-1000 AD). There were good studies of the patterns of thread-wrapping on a few Middle Horizon samples and archaeological recovery of one sample from Middle Horizon context. Three Middle Horizon, Wari khipus have been dated between 780-1024 AD. The principal problem of khipu chronology arises with respect to the dating of Inca samples. Thirty-one samples of Inca khipus from museums in the USA, Latin America and Germany have been analysed. The samples were analysed by the accelerator mass spectrometry technique at three laboratories. About half of the samples analysed at the University of Georgia have been analysed twice to get a higher precision. Most of the samples have been dated from Late Horizon times to the early Colonial period, 1500-1600 AD. One of the samples was dated to the beginning of the Late Horizon 1390-1423 AD and another sample was even earlier, i.e. 1188-1282 AD. Unfortunately, the existing calibration data for Inca khipus do not allow high enough sensitivity for precise analysis, thereby requiring a reappraisal of the calibration curve for South America.
khipu, radiocarbon dating, AMS, calibration