Following the worst tragedy in company history on September 11, United conducts a wreath-laying and memorial ceremony at its World Headquarters September 18. The event gives Chicago-area employees an opportunity to formally remember their 18 colleagues lost on Flights 93 and 175. The more than 4,000 participants express their feelings through speeches, poems and music. Company officers and employees also participate that week in memorial ceremonies at the World Trade Center in New York and at the site in Shanksville, Pennsylvania, where Flight 93 crashed.