Throughout the centuries the territory of modern Ukraine has always been crossed by valuable trade routes and some of the most important transportation corridors of the Eurasian continent. Before even the emergence of the ancient Kyivan Rus civilisation the Dnieper River was the main artery linking the Vikings and the Greeks from the Baltic to the Black Sea. Ukraine was also a station post along the Silk Route connecting the towns of medieval Europe with central Asia, Mongolia and China. To date, 273,700km of highways, 22,510km of railway, 4,500km of waterways, 250,000 different flight paths and 42,900km of pipelines form Ukraine's transportation network. Ukraine is among the world's largest transporters of natural gas.