This is Plovdiv’s oldest church and one of its most beloved. Dedicated to Emperor Constantine the Great and his mother, Helena, it was built on the spot where two Christian martyrs were beheaded in the year 304. Admire marvellous frescoes and a colourful carved ceiling in the exterior colonnade, and a baroque-style Viennese iconostasis and religious art spanning the 15th to 18th centuries inside. The separate bell tower, bright white with a coppery cap, stands 13m tall.