The sanctuary on the island of Keros takes the form of deposits of broken marble vessels and figurines, probably brought severally for deposition from elsewhere in the Cyclades. These acts of devotion have now been accurately dated, thanks to Bayesian analyses of the contemporary stratigraphic sequence on the neighbouring islet of Dhaskalio. The period of use—from 2750 to 2300 cal BC—precedes any identified worship of gods in the Aegean and the site is among the earliest ritual destinations only accessible by sea. The authors offer some preliminary thoughts on the definition of these precocious acts of pilgrimage.