The Patriarchal Cathedral of St. Alexander Nevski is the largest Orthodox temple on the entire Balkan Peninsula.
The cornerstone of the St. Alexander Nevski cathedral was laid on February 19, 1882. At the same time, two texts were placed in the temple’s foundations: one was engraved on a metal plate and the other was written on parchment. The historical events of 1877-1878 will be preserved forever in them.
The official sanctification of the temple happened in 1924. Since the temple has three thrones, the illumination seat is on three consecutive days – 12, 13 and 14 September.
Ref.: https://www.cathedral.bg/