Those campaigning against the wall have few allies. Yoshihiro Murai, the governor of Miyagi, is in favour, while the prime minister, Shinzo Abe, told a recent residents‘ forum that walls offered the best protection against a tsunami. His wife, Akie, has cautiously allied herself with the sceptics, warning of the damage so much concrete could do to ecosystems and tourism.

The 3,000 people of Fudai village owe their lives to a 15-metre wall that was dismissed as a waste of money when it was built, at the then mayor’s insistence, in the 1980s. But it was the exception. Most sea walls provided inadequate protection against the March 2011 tsunami. In Kamaishi, the waves simply smashed through the city’s sea wall, then the largest in the world. Concrete barriers offered little or no resistance, and may even have caused deaths among people lulled into thinking they were safe.

„Sea walls have the potential to save lives wherever they are built, provided the tsunami does not exceed the simulated height and runup pressures,“ said Dimmer. „The problem is that you can’t predict how high the next tsunami will be, so sea walls can never give you 100% security. There will always be a risk, no matter how high you build them.“

Campaigners estimate that it will take Japan’s taxpayers a quarter of a century to pay the bill for sea wall construction, which could eventually cover 9,000 miles of the country’s coastline. But the debate is about more than cost. Until each locality decides whether to proceed with the plan, no construction can begin on sites considered vulnerable totsunamis.

„I don’t want the rest of the world to think of Japan as a concrete fortress,“ said Abe. „The tsunami was a force of nature, so I can forgive it for the destruction and misery it caused. But for humans to ruin their own environment … I can never forgive that.“