Three key late comers in prehistoric Greece: steppe ancestry, horses and millet

A review paper at Archaeological and Anthropological Sciences posits that millet and horses arrived in what is now Greece together during the Bronze Age (see here). The author suggests that they may have been introduced via contacts with cultures to the north/northeast of Greece or directly by migrants from the Eurasian steppe. Considering the recent discovery via ancient human DNA that steppe ancestry also spread into the southern Balkans and Mycenae during the Bronze Age (see links below), I'd say the latter scenario is much more likely. I'd also add that millet and horses were probably part of an economic and cultural package expanding along with early Indo-European speakers throughout Eurasia at the time (note, for instance, how important horses are to the early Indo-European pantheon). Here's the review abstract. Emphasis is mine.

Abstract: Archaebotanical evidence for Panicum miliaceum is reviewed for prehistoric Greece including published and unpublished recent finds, providing a basis for exploring the context of the appearance of millet in Greece, the timing of its introduction and cultivation, and its significance in terms of contacts, movement of people, and cultural identity as expressed through culinary practice and food consumption. To this end, the archaeobotanical record is examined together with human isotopic, archaeozoological, and artefactual evidence. Millet is introduced to the northern part of Greece sometime during the end of the 3rd millennium bc and established as a widely used crop during the Late Bronze Age. Isotopic evidence suggests that millet consumption during the Late Bronze Age was not widespread but confined to certain regions, settlements, or individuals. Millet is suggested to reach Greece from the north after its spread westwards from China through Central Asia and the steppes of Eurasia. The timing of the introduction of millet and the horse in northern Greece coincide; the possibility therefore that they are both introduced through contacts with horse breeding cultures cultivating millet in the north and/or northeast is raised. Intensified contact networks during the Bronze Age, linking prehistoric northern Greece to central Europe and the Pontic Steppes, would have opened the way to the introduction of millet, overland via river valleys leading to the Danube, or via maritime routes, linking the Black Sea to the north Aegean. Alternatively, millet could have been introduced by millet-consuming populations, moving southwards from the Eurasian steppes.

Valamoti, S.M., Millet, the late comer: on the tracks of Panicum miliaceum in prehistoric Greece, Archaeol Anthropol Sci (2016) 8: 51. https://doi.org/10.1007/s12520-013-0152-5

See also...

Steppe invaders in the Bronze Age Balkans

Steppe admixture in Mycenaeans, lots of Caucasus admixture already in Minoans (Lazaridis et al. 2017)

Late PIE ground zero now obvious; location of PIE homeland still uncertain, but...