Three historical places in Istanbul have recently been renovated. Serefiye Cistern was built by Roman Emperor Theodosius II between 428 and 443 to store water supplied by the Valens Aqueduct. The Bulgarian Church is the oldest Slavic Orthodox Church with some six million members in the Republic of Bulgaria and between 1.5 and two million members in a number of European countries. Tekfur Palace was constructed during the late 13th or early 14th centuries as part of the Blachernae palace complex, where the Theodosian Walls join with the later walls of the suburb of Blachernae.