"The fumie...were brass images, sometimes set in wooden boards, depicting either the Christ or Mary. Every single person that lived in Nagasaki was ordered..."

"... to go through the [annual] practice of stepping on the fumie.... 'It was an obligation, the commoners, the samurai, the Buddhist monks, even sick people couldn't miss it - they would bring the wooden board to their house. Every single person had to do this... It was quite well thought out because at the time, Christians relied a lot on images. People prayed in front of an image - Mary, Jesus - so many thought that part of the God was inside the image. It was a link to the divine... for them to tread upon this, was something very fearful.'... The Christians who refused to tread on the fumie were killed, or, more commonly, tortured. 'They would sometimes torture them by hanging them over a pit filled with excrement. They would cut slits around their temples to release [the pressure] so they wouldn't die'.... In 1858, the fumie practice was abolished in Nagasaki. In 1873, Japan's long ban on Christianity was finally lifted - more than two centuries after it was first put in place. 'When Japan opened up its borders again, around 20,000 Christians reappeared and came out of hiding,' said Mr Mullins. 'In that sense, the [fumie] policies were effective. You'd gone from around 500,000 to 20,000 Christians.'...  'It is only because some made an existential decision to trample on the fumie, despite their belief that this action was gravely sinful, that Christianity in Japan was able to survive.'"

From "The Japanese Christians forced to trample on Christ" (BBC). This article coincides with a visit to Nagasaki by Pope Francis.