The height of Tokyo Skytree — 634 meters — has symbolic meaning for the area known long ago as Musashi, covering Tokyo and parts of Saitama and Kanagawa, because the figure's syllables can stand for 6 ("mu"), 3 ("sa") and 4 ("shi").
But 610, 628, 633, 645 and even 666 meters were all considered as the final height at one point, according to its builder, Tobu Railway Co. The Skytree project originally began with 610 meters as the tower's planned height, but after the 600-meter-tall Canton Tower in China opened in September 2010, the 10-meter advantage was not considered enough. Higher levels were considered, including 628, the year nearby Sensoji Temple was built.
645, the year of the Taika Reforms, in which Emperor Kotoku established political doctrines, was also a candidate.
The 633-meter plan stemmed from the 6-3-3 school year system, for elementary, junior high and high schools.
Organizers believed it would represent the growth of a child. But that idea was later dropped, reportedly because it was felt that foreign visitors with different school systems would have a difficult time understanding the meaning.
A 666-meter Skytree was also considered. This would have made it exactly double the height of Tokyo Tower. However, Skytree could only reach a maximum of 640 meters structurally.
"We wanted to open as the world's tallest (tower). There was conflict over not making it 640 meters, but everyone eventually settled on 'musashi' because they felt a sense of attachment to it," a Tobu Railway official said.