A 39,000 year old hashtag etching has been found in a Mediterranean cave, beneath layers of sediment containing Neanderthal tools. The markings were undoubtedly created on purpose (i.e., not the result of sedimentary or geologic forces), and it is very likely that they were created by Neanderthals (not Homo sapiens). The location and dating of the etchings support this hypothesis, since Homo sapiens had not yet made it to Gibraltar at the time the etchings were made.

What were these engravings for? They are about the size of a Frisbee and are etched into the surface of flat, table-like rock in a prominent location in the cave; further, the pattern took over 300 strokes to complete*. Were Neanderthals somehow marking territory lines? Was it a primitive form of artwork? Or were these intelligent humans (for Neanderthals were, indeed, humans) simply playing their ancient version of tic-tac-toe?

Thus remains one of the most intriguing questions that exists: what was it like to be a Neanderthal?

* In case you were wondering how we know that, scientists tried recreating the marks using original Neanderthal stone tools.