Rousse Province (also literated Ruse) is situated in the northeastern part of Bulgaria. The province includes a total of eight municipalities – Rousse, Byala, Ivanovo, Tzenovo, Borovo, Slivovo Pole, Dve Mogili and Vyatovo, and has the regions of Silistra and Razgrad neighboring on the east, Targovishte on the southeast and Veliko Tarnovo on the west. Its northern border reaches the Danube’s riverside and merges with the national border with Romania. The district's administrative centre is the city of Rousse, the largest Bulgarian city along the river banks of the Danube River. Rousse is also most popular for its bridge across the Danube River since it is the only cross-over point between Bulgaria and Romania. The Rousse region is an important Bulgarian and European transport junction. It combines all means of transport available. Two of the Pan-European transport corridors cross the district. The port of Rousse is Bulgaria's biggest river port and represents both river and marine transportation. The Danube Bridge, which as of January 2007 is free of customs control at Gyurgevo's and Rousse's border checkpoints facilitates all means of land transportation. And last but not least the crossroad of the E-70 road and several national roads and railways extend across the region. The closest international airport is Bucharest (Romania), which is approximately 100 km from the city of Rousse. Varna Airport is also a convenient option (200 km), though smaller. Bulgaria's capital city, Sofia, is around 320 km from Rousse. The region favors the benefits of the Yantra and Rusenski Lom rivers flowing through the region, providing very good conditions for agriculture. There are several protected nature areas across the Rousse region – the Rusenski Lom Nature Park (a marvelous valley of the Rusenski Lom River), the exceptional rock formations near the villages of Pisanets and Mechka, and the 'Orlova Chuka' cave near the town of Dve Mogili. The latter is the second longest cave in Bulgaria and believed to have been inhabited by humans thousands of years ago. There are also about 250 Thracian grave mounds dating back to the IV century BC. A fascinating silver treasure was found in 1974 in one of the graves near the village of Borovo. Ancient remains of Roman fortresses along Danube's river bank were found near the villages of Krivina, Marten, and Rousse and add up to the historical value of the region. The region's list of historical sights also includes the Ivanovo cliff churches, which are part of UNESCO's List of World Cultural Heritage. The history of the Rousse region has been strongly related to transport. Back in 1886, Bulgaria's first railroad was built, connecting the ports of Rousse and Varna. The city of Rousse is also popular for its architecture. Being border town during the 18th and 19th centuries, it not only gained wealth and developed long-standing trade relations, but was also strongly influenced by the European culture and lifestyle. A present example for this cultural interaction is the city's architecture reminding of Vienna. Unlike many other Bulgarian cities, Rousse has managed to preserve many of those distinctive buildings, most of them located downtown on Alexandrovska Street.