The uniqueness of the language underscores the mystery of the origins of the Basques. Some scholars have suggested that they may even be the direct descendants of Cro-Magnons and the Upper Paleolithic cave painters active in Southwestern Europe about 15,000 years ago. Until the Middle Ages Basques were an enclaved, pastoralist people, fierce in resisting the intrusions of outsiders and regarded as barbarians by them. Romans, Goths, Franks, and Moors all controlled parts of the Basque Country without ever quite subjugating it. It was a Basque force that attacked Charlemagne's rear guard as it traversed the Pass of Roncesvalles, killing Roland and giving rise to the famous epic The Song of Roland. After A.D. 1000 the several Basque regions came increasingly under the influence of emerging European kingdoms and duchies. Subsequently the embryonic states of England, France, and Spain fought for control over the regions, which frequently became pawns in larger power plays. Sovereignty over the various Basque regions shifted according to the fortunes of battle or the whims of marital alliances among Europe's royalty. Basques retained, however, a considerable degree of autonomy in their own affairs, codified in written fueros or charters. This relative autonomy was reflected in the custom whereby the monarchs of Castille, upon ascending the throne, were required to travel to the town of Guernica to swear beneath a sacred oak to respect Basque laws. Coastal Basques were Europe's earliest whalers. Their shipbuilding and navigational skills made them Iberia's most noted seafarers. By the early fifteenth century (and possibly earlier) Basques were crossing the Atlantic for whaling and cod fishing off the Labrador coast. Basques crewed the ships of Columbus and Magellan. (The Basque Elcano was the first to circumnavigate the globe.) Basque mariners, mercenaries, merchants, and missionaries swelled the ranks of Spain's colonial elite, providing much of the shipping in the American trade and capital for development of the colonies and becoming major figures in both the civil and ecclesiastical administrations. The French Revolution, with its strong centralist tendencies, destroyed the political autonomy of Lapurdi, Behe-Nafarroa, and Zuberoa. Many of their residents resisted and were sent to the guillotine or to concentration camps. In the nineteenth century Basques fought on the losing side of Spain's two Carlist Wars, relinquishing much of their political autonomy in defeat. This, coupled with the late nineteenth-century influx of Spanish workers to Basque industries, which threatened to make Basques a minority in their homeland, caused concern. By 1900 a modern Basque nationalist movement had emerged to confront Madrid's policies in the Basque country. The nationalists contested elections when allowed to do so, gaining control of many municipalities and the provincial assemblies of Gipuzkoa and Bizkaia. When the Spanish Civil War erupted in 1936, those two provinces remained loyal to the republic, fielded an army, and elected an autonomous government that issued passports and coined its own currency. Within nine months the Basques were defeated by Franco, many were executed or imprisoned, thousands were exiled, and the Basque government had been removed to Paris. During the Franco years there was systematic repression of Basque culture. Consequently, in the late 1950s disaffected Basque youths founded an organization known as "ETA" (Euskadi ta Azkatasuna, or "Basque Country and Freedom") with the goal of complete independence from Spain. Its opposition to Franco escalated into violence, providing Europe with one of its most virulent terrorist movements. Franco's death in 1975 ushered in an era of democracy in Spain. Mainline Basque nationalists collaborated in the framing of a new constitution that accorded considerable autonomy to the regions.