Childe and Ernst Wahle. One of Wahle's students was Jonas Puzinas, who became one of Marija Gimbutas's teachers. Gimbutas, who acknowledged Schrader as a precursor, painstakingly marshalled a wealth of archaeological evidence from the territory of the Soviet Union and the Eastern Bloc that was not readily available to Western scholars, revealing a fuller picture of prehistoric Europe. Overview When it was first proposed in 1956, in The Prehistory of Eastern Europe, Part 1, Gimbutas's contribution to the search for Indo-European origins was an interdisciplinary synthesis of archaeology and linguistics. The Kurgan model of Indo-European origins identifies the Pontic–Caspian steppe as the Proto-Indo-European (PIE) urheimat, and a variety of late PIE dialects are assumed to have been spoken across this region. According to this model, the Kurgan culture gradually expanded to the entire Pontic–Caspian steppe, Kurgan IV being identified with the Yamnaya culture of around 3000 BC. The mobility of the Kurgan culture facilitated its expansion over the entire region and is attributed to the domestication of the horse followed by the use of early chariots. The first strong archaeological evidence for the domestication of the horse comes from the Sredny Stog culture north of the Azov Sea in Ukraine, and would correspond to an early PIE or pre-PIE nucleus of the 5th millennium BC. Subsequent expansion beyond the steppes led to hybrid, or in Gimbutas's terms "kurganized" cultures, such as the Globular Amphora culture to the west. From these kurganized cultures came the immigration of Proto-Greeks to the Balkans and the nomadic Indo-Iranian cultures to the east around 2500 BC. Kurgan culture Cultural horizon Gimbutas defined and introduced the term "Kurgan culture" in 1956 with the intention of introducing a "broader term" that would combine Sredny Stog II, Pit Grave, and Corded ware horizons (spanning the 4th to 3rd millennia in much of Eastern and Northern Europe). The Kurgan archaeological culture or cultural horizon comprises the various cultures of the Pontic–Caspian steppe in the Copper Age to Early Bronze Age (5th to 3rd millennia BC), identified by similar artifacts and structures, but subject to inevitable imprecision and uncertainty. The eponymous kurgans (mound graves) are only one among several common features. Cultures that Gimbutas considered as part of the "Kurgan culture": Bug–Dniester (6th millennium) Samara (5th millennium) Khvalynsk (5th millennium) Dnieper–Donets (5th to 4th millennia) Sredny Stog (mid-5th to mid-4th millennia) Maikop–Deriivka (mid-4th to mid-3rd millennia) Yamnaya (Pit Grave): This