Interesting as these are from an archeological perspective, I was also intrigued by the possibility of a Tolkien link here, given his description of the Stone of Erech:
". . . a black stone, round as a great globe,
the height of a man, though its half
was buried in the ground" (LotR.820)
Cf. the description of the stones from wikipedia,** which notes that the largest are "over 2 meters (6.6 ft) in diameter . . . Most are sculpted from gabbro, the ganitic equivalent of basalt" -- and indeed, although lightened by weathering several of those pictured in the BBC article are in fact black, though not the smooth shiny black I'd imagined while reading Tolkien's passage.
Could the Bolas, as they are locally known, have actually inspired Tolkien's Stone of Erech? As far-fetched as that first appears, it actually could have been possible. The stones were first discovered in the 1930s, and drawn to the attention of the archeological community when Doris Stone published an article about them ("A Preliminary Investigation of the Flood Plain of the Rio Grande de Terraba, Costa Rica") in a 1943 issue of the journal AMERICAN ANTIQUITY (vol. 9, no. 1; pages 74-88). I haven't yet had a chance to read this piece (that awaits my next visit to Suzzallo-Allen), but checking the Bodleian's online catalogue I note that they do have this issue, and the first mention of Tolkien's Stone seems to come about a year later, in October/November 1944 (cf. HME.VIII.234 & 262). And we know that Tolkien was interested in archeology, and subscribed to ANTIQUITY magazine (the British, not the American journal).***
So, possibly coincidental, but intriguing nonetheless -- and it might explain the oddity of the Stone of Erech, which seems distinctly unlike all the neolithic monuments scattered throughout the story. I'll post a follow-up after I've seen Doris Stone's original piece and find out whether it included any illustrations.
*I don't know if that extends to the people. Let's hope not.
***one of the mailers an issue came in is preserved among his manuscripts in the Bodelian (A29/1, fol. 1)
I have now read Stone's original article, the most interesting feature of which was her stressing that stone balls have been found widely distributed, all the way from Tennessee through the Caribbean (Haiti, Puerto Rico) to the southernmost tip of South America. However, most of these are hand-sized, and probably used in games.
Aside from a single two-foot-diameter stone ball found at Veracruz, all the giant balls seem to be limited to the Terraba region of Costa Rica. Stone does include an evocative picture of one of the largest stones still half-buried in the ground (Plate IV, image f, opposite page 77) that could have inspired Tolkien's description of the stone at Erech.
Could have. But that one image is simply one among many accompanying an article whose rather dull title conceals the interesting topic within. All things considered, without some more direct tie it seems unlikely that Tolkien would have stumbled across this image or essay. Interesting though it is to find that this detail from his fantasy world has a real-world parallel, in all probability it's just co-incidence.
But if anyone comes across any collaboration, I'm listening . . .