In 1934-37 and 1947 the archaeological remnants of the medieval town were excavated. The most striking find was the basement of the eight-pillared Church of St. Basil, founded by Vladimir the Great and named after his patron saint. As the church was one of the largest in Kievan Rus', it took twenty years to complete it. Before the Mongol invasion the church housed the relics of the first East Slavic saints, Boris and Gleb, but their subsequent fate remains a mystery. The ancient Cossack military monastery, the Mezhyhirskyi Monastery, stood not too far away from the city.