Construction of the monument began on 23 January 1974 under architect Georgi Stoilov, a former mayor of Sofia and co-founder of the Union of Architects in Bulgaria.[1] Trinitrotoluene (TNT) was used to level the peak into a stable foundation, reducing the mountain's height from 1,441 metres (4,728 feet) to 1,432 metres (4,698 feet).[1] More than 15,000 cubic metres of rock were removed in the process.[1] The monument was built at a cost of 14,186,000 leva, which by today's[when?] rates is roughly equivalent to US$35 million.[clarification needed][1]