A recent paper discussed at Bernard's blog examines the similarities between stone monuments (especially anthropomorphic stele) in the Mediterranean region and those on the Steppe. The Old European culture blog makes a similar more focused comparison of such stone monuments in the Balkans and Ireland.
These stylistic connections are too striking an idiosyncratic to be mere coincidences. But, when did these styles migrate, who was associated with that migration, and in what direction did the cultural transfer take place? Were these aspects of physical culture associated with a particular language or language family, and if so, which one? Is this a case of "pots are people" or were these aspects of physical culture transmitted without any major demic migration?
Consider the many cultural connections between the Balkans and the Irish that are explored at the Old European culture blog. The most recent and obvious source for linguistic similarities would be via proto-Celtic or proto-Celtic/Italic which probably originated not far from the Balkans and then migrated to Ireland evolving into Celtic en route, arriving there something within the last 2500 to 3000 years ago. Many of the cultural objects which are similar could also date to this time period.
Even more recently, but less plausibly, some of these connections could be due to shared exposure to the Roman Empire.
But, if there are older cultural links, that would suggest connections via some non-Indo-European peoples, such as the first wave Neolithic population, or a latter Copper or Bronze Age transmission. A link via a post-first wave Neolithic population that is pre-Celtic would be particularly interesting because this era of prehistory is still not well understood.
Some scholars have associates the population genetic shift in Western Europe from low frequencies of Y-DNA R1b-M269 to high frequencies of Y-DNA with a culture that was the means by which the practice of making these stone monuments was transferred from the East to Western Europe, via "the Stele people".
It also isn't entirely clear if the pre-Celtic peoples of Western Europe were non-Indo-European, as I tend to believe, or if a pre-Celtic Indo-European language prevailed in the region earlier (although still probably after the first wave Neolithic migration to Western Europe).