Hurricane Katrina, which hit the Gulf Coast in late August 2005, was not only the most disastrous hurricane in U.S. history, it was the nation’s worst single weather disaster. Though not the strongest possible hurricane when it made landfall (Katrina had weakened from a category 5 storm to a category 4 storm just before it struck the Gulf Coast), Katrina was a monster: The storm stretched about 200 miles in diameter, packed winds up to 145 miles per hour, produced torrential rain and huge waves, spawned twisters throughout the region, and pushed up a 28-foot storm surge—a surge usually found only in category 5 hurricanes.

Katrina moved ashore on the Gulf Coast on Monday, August 29. In anticipation of the hurricane, New Orleans, which sits below sea level, had been evacuated. But there were still tens of thousands who stayed—out of necessity (such as law enforcement and healthcare workers), because they were unable to evacuate, or because they chose not to leave. Some 23,000 of those who stayed holed up in the aging Superdome sports arena, which was set up as an emergency shelter. The structure barely withstood the lashing winds of Katrina, which blew off portions of the dome. On Tuesday morning, after Katrina ravaged Louisiana, Mississippi, and Alabama, before weakening as it moved inland, officials and news reporters generally agreed that there was unbelievable damage all along the coast, but New Orleans had “dodged a bullet”: the Big Easy had not taken the worst of it. Gulfport and Biloxi, Mississippi, appeared the hardest hit. The devastation there was astonishing. As reports of damage began to be made, it became clear that about 90 percent of the structures along the Gulf Coast were destroyed and hundreds of thousands of people were displaced by Katrina. The death toll was not known, and officials conceded it would take time to determine. The storm had been so ruinous—of biblical proportions, some said—that rescue and recovery would take weeks and months. Later, when the full extent of damage began to be discovered, the recovery estimates were revised to years.

Later Tuesday, New Orleans’ fate changed: levees that protect the city could not hold back a swollen Lake Pontchartrain; 80 percent of the city filled with water, 25 feet deep. Officials and volunteers could not get flood victims out fast enough, usually plucking them from rooftops or finding them in attics, where survivors sought refuge as waters rose. The city descended into chaos and lawlessness. Heart-wrenching images of human despair filled the media, touching people around the nation. Americans responded with donations of money, goods, and time. The American Red Cross launched the largest mobilization effort in its history. The Federal Emergency Management Agency (FEMA, a part of the Department of Homeland Security [DHS]), the Coast Guard (also part of the DHS), and the U.S. military struggled to keep pace with Katrina’s aftermath all along the coast.

For all the effort, it was widely acknowledged that the government’s response to the disaster was inadequate and late. On Friday, September 2, President George W. Bush said that the results had been unacceptable; he further promised to “make it right.” While politicians and the people spoke out on the subject, some experts said the catastrophe had simply overwhelmed the system: Emergency programs across the nation had been set up to rely on local and state response first, backed by the federal government. In Katrina’s case, the devastation was so great that the localities and states either were not able to respond at all or could not respond with enough help;federal intervention had been needed sooner and in greater measure to alleviate human suffering and protect lives. Government officials all seemed of one accord, however: The fact-finding could wait; the victims could not. Cities and states across the nation sent resources to the Gulf Coast and set up emergency centers to receive storm refugees, whose needs were immediate (water, food, clothing, shelter, medicine, healthcare, and counseling) and long term (jobs, schools, and permanent housing).

On Wednesday, September 7, nine days after Katrina struck, the situation continued to unfold. The size and scope of the tragedy remained to be fully understood. New Orleans ordered a forced evacuation of the holdouts; the city remained flooded with toxic floodwaters as repairs were made in the levees and the hazardous water began to be pumped out. Efforts to reunite families, separated in the chaos, were ongoing. For many days, rescue workers all along the Gulf Coast had moved from house to house to find survivors; now it was a matter of trying to identify and count the dead. The death toll was expected to be in the thousands. The affected area was 90,000 square miles, or about the size of Minnesota. Property damage was projected to be at least $26 billion in insured losses and perhaps twice that amount in uninsured losses. (Katrina had also caused damages as it struck Florida as a category 1 hurricane on August 26; it later moved into the warm waters of the Gulf of Mexico and strengthened before striking the Gulf Coast.)

Katrina’s aftermath was felt in every state of the union: volunteers shored up efforts to assist survivors who were being relocated in an effort to ease the burden on the afflicted region; schools across the nation opened doors to displaced students; fuel prices skyrocketed and natural gas and heating oil prices promised to follow, as offshore rigs and Gulf Coast refineries suffered; and most Americans worried about the government’s response to the catastrophe. The disaster made an impact around the world as well, with some 95 countries offering assistance.

Before Katrina, the deadliest hurricane to strike the United States was an unnamed category 4 storm that struck Galveston, Texas, in 1900. The September 8 storm claimed at least 8,000 lives (some estimates place the number as high as 12,000).

Hurricane strength is measured on the Saffir-Simpson scale, where category 1 is the weakest (with sustained winds of at least 74 miles per hour and a storm surge of 4 to 5 feet above normal) and category 5 is the strongest (with sustained winds of more than 155 miles per hour and a storm surge higher than 18 feet). The United States has been hit by three category 5 storms since record-keeping began. The first was a Labor Day hurricane, which struck the Florida Keys in 1935; 408 people died. The second was Camille, which hit Mississippi and southeast Louisiana in 1969, claiming 256 lives. Hurricane Andrew, which struck south Miami-Dade County, Florida, in late-August 1992, was measured as a category 4 storm at the time, but the National Oceanographic and Atmospheric Agency (NOAA) reclassified it in 2002 as a category 5 storm. Andrew claimed more than 100 lives and devastated a wide area, mostly around the town of Homestead, Florida.