After the September 11, 2001 terrorist attacks that destroyed the World Trade Center, many people wondered if Manhattan’s Financial District-a place that helped coin the American English word “downtown”-could ever recover. Cities throughout the country also questioned whether dense, high-rise districts could be sustained. That same year, San Francisco was reeling from the dot-com collapse as thousands of jobs disappeared, office vacancies climbed to over 20%, and rents eventually fell by over 60%. But within a few years, office demand returned, and these central business districts refilled with workers and activity.