In the devastated northeastern coastal town of Rikuzentakata, a siren sounded at 2.46 pm (05.46 GMT), the exact time the magnitude-9.0 quake struck. A Buddhist priest in a purple robe rang a huge bell at a damaged temple overlooking a barren area where houses once stood.
The tsunami also knocked out the vital cooling systems at the Fukushima Dai-ichi nuclear power plant, causing meltdowns at three reactors and spewing radiation into the air.
Some 100,000 residents who were forced to flee remain in temporary housing or with relatives, and a 12-mile area around the plant is still off limits.