Pskov is situated in northwestern Russia and has internal borders with the Novgorod, Leningrad, Tver and Smolensk Regions as well as external borders with Belarus, Estonia and Latvia. Founded in the 10th century, this is a city rich in history. During the Middle Ages, Pskov was a main stronghold on Russia's northwestern frontier, a capital of a wealthy principality, and one of the largest cities in Europe. In Pskov trade was thriving, the arts were developing rapidly, and the unassailable fortified city walls protected the town and its citizens from the attacks of those attracted by fabulous treasure. Many of the architectural monuments of medieval Pskov can still be seen today. Historical landmarks include beautifully preserved ancient stone building such as the Spaso-Preobrazhensky Cathedral and the 12th century Cathedral of the Spaso-Mirozhsky monastery.