When the project was first announced, however, it seemed that no Russian company wanted to touch it. There were extraordinary engineering challenges, and anything involving Crimea carried the risk of international sanctions. Even more daunting, perhaps, the ultimate project supervisor, known to be a demanding boss, was laying out a rigorous construction schedule.

“The bridge itself is difficult, the scale is huge and it is tough to meet the deadline,” said Oleg Skvortsov, a bridge specialist who led a 50-member expert advisory council. “The deadline was set by the president, so nobody wanted to take the risk.”

Into the breach stepped Arkady R. Rotenberg, a billionaire who has made a career of taking on Mr. Putin’s pet projects. A judo partner with the president since their youth in St. Petersburg, Mr. Rotenberg was also conveniently already under Western sanctions over Crimea because of his status as a member of Mr. Putin’s inner circle.

There is some question whether Mr. Rotenberg volunteered or was pushed. The official version that he voiced himself is that no sacrifice is too great when serving the motherland, plus the bridge would stand as his crowning construction achievement.

“It seems that this is the last big project for me, and I am doing it not to make money,” he told the daily Kommersant in a 2015 interview. “If you permit me to say this, it is my contribution to the country’s development.”

The padding involved in huge government construction projects has often served as the conduit for the Kremlin to enrich its friends. The most notorious recent example was the development of the Black Sea resort city of Sochi for the 2014 Winter Olympics, with costs mushrooming to $51 billion, the most expensive Olympics ever.