Indo-European reaches from Ireland to Bengal, and its recognition in the late eighteenth century created historical linguistics as a field. William Jones, speaking in Calcutta in 1786, observed that Sanskrit bore to Greek and Latin a resemblance stronger than accident could explain, and proposed that all three had sprung from a common source which perhaps no longer exists. He was not the first to notice the resemblance, but the programme he described is what the nineteenth century then carried out. Regular sound correspondences were worked out, the comparative method was built to formalise them, and by the end of the century a reconstructed ancestor existed on paper.
Today the family holds around 450 languages and more speakers than any other, a fact that owes as much to colonial expansion as to anything older. Its branches include Indo-Iranian, Greek, Italic, Celtic, Germanic, Balto-Slavic, Armenian, Albanian, and the extinct Anatolian and Tocharian groups. Anatolian, recovered from Hittite cuneiform tablets only in the twentieth century, forced a substantial revision of the reconstruction, which is a useful reminder that a reconstructed proto-language is a hypothesis maintained under evidence rather than a discovered artefact.