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As the long years passed the situation changed. The ancient Adûnaic of Númenor became worn down by time - and by neglect. For owing to the disastrous history of Númenor it was no longer held in honour by the 'Faithful' who controlled all the Shorelands from Lune to Pelargir. For the Elvish tongues were proscribed by the rebel Kings, and Adûnaic alone was permitted to be used, and many of the ancient books in Quenya or in Sindarin were destroyed. The Faithful, therefore, used Sindarin, and in that tongue devised all names of places that they gave anew in Middle-earth. Adûnaic was abandoned to unheeded change and corruption as the language of daily life, and the only tongue of the unlettered. All men of high lineage and all those who were taught to read and write used Sindarin, even as a daily tongue among themselves. In some families, it is said, Sindarin became the native tongue, and the vulgar tongue of Adûnaic origin was only learned casually as it was needed. The Sindarin was not however taught to aliens, both because it was held a mark of Númenórean descent and because it proved difficult to acquire - far more so than the 'vulgar tongue'. Thus it came about that as the Númenórean settlements increased in power and extent and made contact with Men of Middle-earth (many of whom came under Númenórean rule and swelled their population) the 'vulgar tongue' began to spread far and wide as a lingua franca among peoples of many different kinds. This process began in the end of the Second Age, but became of general importance mainly after the Downfall and the establishment of the 'Realms in Exile' in Arnor and Gondor. These kingdoms penetrated far into Middle-earth, and their kings were recognized beyond their borders as overlords. Thus in the North and West all the lands between the Ered Luin and the Greyflood and Hoarwell, became regions of Númenórean influence in which the 'vulgar tongue' became widely current. In the South and East Mordor remained impenetrable; but though the extent of Gondor was thus impeded it was more populous and powerful than Arnor. The bounds of the ancient kingdom contained all those lands marked in maps of the end of the Third Age as Gondor, Anórien, Ithilien, South Ithilien, and Rohan (formerly called Calenardhon) west of the Entwash. On its extension at the height of its power, between the reigns of Hyarmendacil I and Rómendacil II (Third Age 1015 to 1366) see The Lord of the Rings Appendix A p.325. The wide lands between Anduin and the Sea of Rhûn were however never effectively settled or occupied, and the only true north boundary of the Kingdom east of Anduin was formed by the Emyn Muil and the marshes south and east of them. Númenórean influence however went far beyond even these extended bounds, passing up the Vales of Anduin to its sources, and reaching the lands east of the Forest, between the River Celon(Running) and the River Carnen (Redwater).
Within the original bounds of the Kingdoms the 'vulgar speech' soon became the current speech, and eventually the native language of nearly all the inhabitants of whatever origin, and incomers who were allowed to settle within the bounds adopted it. Its speakers generally called it Westron (actually Adúni, and in Sindarin Annúnaid). But it spread far beyond the bounds of the Kingdoms - at first in dealings with 'the peoples of the Kingdoms', and later as a 'Common Speech' convenient for intercourse between peoples who retained numerous tongues of their own. Thus Elves and Dwarves used it in dealings with one another and with Men
'Of Dwarves and Men' HoME 12