Which US city is famous for jazz and Mardi Gras?

New Orleans, and the reason jazz began there rather than anywhere else is a specific piece of local history. Under French and Spanish rule enslaved people were permitted to gather on Sundays at Congo Square and to keep drumming and dancing traditions that were banned across most of the American South - so West African rhythm survived in one city in a way it did not elsewhere.

That met European harmony, brass instruments left cheap and plentiful after the Civil War, the Caribbean influence of Haitian refugees, and a large free Creole population with formal musical training. Jazz is the collision of those things in one port, and it travelled up the Mississippi and out through Storyville's closure in 1917, which put a great many musicians on the road.

The city sits mostly below sea level in a bowl, protected by levees, subsiding as drained soil compacts, and losing the coastal wetlands that used to absorb storm surge - Louisiana loses something like a football pitch of land an hour. Hurricane Katrina in 2005 killed over 1,300 people, and the failure was largely engineering rather than weather: the levees were breached in more than fifty places, and the subsequent investigation described it as the worst civil engineering disaster in American history.