A massive wildfire that destroyed homes and forests receded Monday as a multinational airborne effort beat back flames that at one point threatened Athens' northern suburbs and raged near the ancient battleground at Marathon.

As winds died down late Monday, Greek Fire Brigade spokesman Yiannis Kappakis said there were "no significant active fronts" left of the fire, which for days has sent a pall of smoke over the capital, plunging parts of it into a brown half-light.

Kappakis said more than 1,000 firefighters and soldiers would remain on duty in case the blazes revived.

Click here for photos.

"The danger of the fires flaring up again is not yet over," he said. Since Saturday the fire has razed some 21,000 hectares (51,890 acres) of pine forest, olive grove, brush and farmland, according to the European Commission's European Forest Fire Information System. Greek officials say 150 homes were damaged.

Experts warned it would take generations to replace the lost forests, many of which were burnt beyond the hope of natural regrowth.

Thousands of people were forced to flee their homes, and elderly nuns were evacuated from the threatened convent of Saint Ephrem near the coastal town of Nea Makri — carrying the saint's relics with them.

"The flames were 30 meters (100 feet) high," said one of the nuns evacuated, wearing a black habit and a surgical mask to ward off the smoke and grit. "Thankfully they came and rescued us."

At least five people were treated for burns and several dozen reported breathing problems, but no injuries were serious, the Health Ministry said.

Other major fires still burned near the coastal town of Porto Germeno, northwest of Athens, and near villages on the Evia island, east of the capital.

Nineteen water-dropping planes and helicopters — including aircraft from Italy, France and Cyprus — unleashed some 14,000 tons of water on Monday that helped contain the biggest blaze near Athens.

The European Commission said in a statement it was the biggest coordinated emergency operation this year.

Before the blaze was contained, flames tore down a hillside toward houses near coastal Nea Makri, where volunteers with water-soaked towels wrapped around their necks beat back the flames with tree branches.

Fires also threatened the ancient fortress town of Rhamnus, home to two 2,500-year-old temples.

Officials have not said what started the fires. Hundreds of forest blazes plague Greece every summer and some are set intentionally — often by the unscrupulous land developers or animal farmers seeking to expand their grazing land.

Many have said Greece's conservative government showed it had learnt little from the wildfires of 2007 — the Mediterranean country's worst in decades — which killed 76 people and laid waste some 679,500 acres.

"A complete overhaul is required in the way we deal with forest fires ... There is no sign the (government) is moving the right direction," said Dimitris Karavellas, director of the environmental group WWF in Greece.

He said state planners made insufficient use of volunteer groups and failed to crackdown on rogue developers who build homes illegally in burnt forest areas.

"A lot of the affected areas have been burned several times, which means these areas will not rejuvenate by themselves," Karavellas said.

Government spokesman Evangelos Antonaros said the firefighting effort was "well coordinated."

"From the first moment, (we had) the presence of personnel on a large scale," he said, also promising that all burnt forests would be replanted and protected from development.

Prime Minister Costas Karamanlis visited a fire-plane base to thank pilots who he said "surpassed the limits of human endurance."

"Continue your work and close your ears to those few who from a safe position for their own expediencies attempt (to criticize) everything," he said. "The entire Greek nation supports you and is grateful."

Greece's National Weather Service said strong winds are expected to ease Tuesday.