Thousands of bleatingbleating merino sheep choked the cobbled streets of the historic town of Salamanca on Sunday, as Spanish farmers revived ancient livestock migration routes to winter pastures. Traffic ground to a halt as 3'000 sheep -accompanied by shaggy dogs, donkeys and oxen -threaded through the centre of the central Spanish town of two universities, two cathedrals and many palaces. They were heading from northern mountains to warmer southern pastures for the winter months. We are here to stake our claim to the droving routes which are being destroyed, said shepherdess Maria Eugenia, leaning on her crook as sheep nibbled roadside bushes and plants. She had walked with her 1'500 sheep 400 kilometres (250 miles) from their cool summer pastures in Spain's northern Picos de Europa mountain range to Salamanca. Wool was the lifeblood of Spain's domestic economy in the Middle Ages. Scores of ancient migratory routes criss-crossed the country, stretching thousands of kilometres. But in modern times road and rail networks have cut across the ancient paths, or canadas, forcing many shepherds to abandon these routes or use trucks to transport stock. This tradition disappeared for 50 years because of the railways and roads which carved up the pathways, said Jesus Garzon, president of the Consejo de la Mesta, a society formed in the 13th century to govern the droving routes. Garzon said Spanish shepherds revived the annual migration, or transhumance, 10 years ago, after the world summit on sustainable development in Rio de Janeiro called on nations to preserve their cultural heritage. For eight years, shepherds drove their sheep through the centre of Madrid, but now they boycott the Spanish capital because they say the government refuses to protect their routes, he said. We have to keep preserving the historic traditions, which are the only ones which last, Garzon said. This has been taking place for 8'000 years in Spain, and even longer elsewhere. Garzon said preserving the routes would bring environmental benefits, including conservation of rare indigenous species of plant and wildlife, such as the lynx or wolf.