In Sakai, Osaka Prefecture, two things are certain: You're never far from the remains of dead people and you're never far from a knife. The two are connected, but not in the way you might think.

Historically an important seaport with a current population of around 830,000, Sakai is conspicuous from the air owing to its massive keyhole-shaped burial mounds ringed by moats and a wall of trees and hemmed in by urban sprawl.

These burial grounds, which were built over hundreds of years beginning in the third century, helped put Sakai on the map — literally — attracting legions of laborers and skilled craftspeople.