Japan must rebuild dozens of ravaged coastal communities, shut down the crippled Fukushima Dai-ichi nuclear-power plant and decontaminate radiated land so it is inhabitable again.
These are enormous burdens on a country already straining under the weight of an aging, shrinking population, bulging national debt and an economy that's been stagnant for two decades.
Prime Minister Yoshihiko Noda reminded the Japanese people that they have overcome many disasters and difficulties in the past and pledged to rebuild the nation so it will be "reborn as an even better place."
"Our predecessors who bought prosperity to Japan have repeatedly risen up from crises, every time becoming stronger," Noda said at a ceremony at the National Theater attended by the emperor and empress.
Later, he told a news conference he hoped to see the disaster-hit areas fully rebuilt when "babies born on the day of the disasters turn 10 years old."
The earthquake was the strongest recorded in Japan's history, and set off a tsunami that swelled to more than 65 feet in some spots along the northeastern coast, destroying tens of thousands of homes and causing widespread destruction.
All told, some 325,000 people are still in temporary housing. While much of the debris along the tsunami-ravaged coast has been gathered into massive piles, only 6 percent has been disposed of through incineration.
Very little rebuilding has begun. Many towns are still finalizing reconstruction plans, some of which involve moving residential areas to higher, safer ground - ambitious, costly projects.
In Rikuzentakata, which lost 1,691 residents out of its pre-quake population of 24,246, a siren sounded at 2:46 p.m. and a Buddhist priest in a purple robe rang a huge bell at a temple overlooking a barren area where houses once stood.
At the same moment in the seaside town of Onagawa, people facing the ocean pressed their hands together in silent prayer.
Memorial services continued into the night. In Ishinomaki, survivors lit some 2,000 candles to mourn for the victims.