In the 17th and 18th centuries the principal Russian interest in Siberia was the highly profitable fur trade. Great quantities of Siberian furs were exported, first to Europe and later to China. During this period the Russian population of Siberia remained small, limited by difficult communications, harsh climatic conditions, and restrictions on migration from European Russia. The Trans-Siberian Railway greatly influenced the composition and size of the population of Siberia. After the railroad’s completion in the early 1900s, Russian people migrated to Siberia in much larger numbers than before, greatly increasing Russian presence in the region. Tsar Alexander III conceived of the railroad in the late 19th century, and construction on several sections took place simultaneously. The construction of the Circumbaikal Railway as part of Trans-Siberian Railway (the section from Port Baikal on the south-western shore of the lake) to Mysovaya Station (on the south-eastern shore) took 4 years. Ancient crystal rocks, granite, gneiss, gabbro, diabases, possess enormous strength; the steep rocky shores precipitously go under water, forcing railroad builders to make excavations and niches in rocky cliffs, and to construct arches and tunnels. The railway is 84 km long. It includes not only Russian engineering design of that time but also the hard work of Russian, Polish, Italian and English workers. The Circumbaikal Railway needed 200 bridges and 33 tunnels. Within the 56-mile section from Kultuk to Port Baikal alone there are 48 arches and tunnels. And how many bridges and supporting walls! It is no coincidence that this part is rightly regarded as the museum of Russian engineering thought, and foreign tourists respectfully name it the golden buckle of the Great Siberian Trail.