Major League Baseball will mark the 18th anniversary on the terrorist attacks of Sept. 11, 2001, on Wednesday with tributes, special caps and base markers.

Games will be played in 15 cities on Wednesday, and each ballpark is scheduled to hold pregame ceremonies and a moment of silence to mark 9/11.

"All of our clubs have a commitment to honoring those whose lives we lost and to ensuring that we don't forget," said Melanie LeGrande, MLB's vice president of social responsibility, told "We're preserving the legacy for those who perished on that day."

The New York Mets will host the Arizona Diamondbacks on Wednesday night and have invited first responders to join them on the field before the game. Both teams will wear NYPD and FDNY caps during batting practice.

Game caps worn by players, coaches and umpires will have 9/11 ribbon patches on the side. The Toronto Blue Jays will wear special caps recognizing both the United States and Canada. The bases will have the message "We Shall Not Forget" on them.

MLB said all of the royalties from the sales of the special caps will be donated to the National September 11 Memorial & Museum in New York, the Flight 93 National Memorial in Shanksville, Pa., and the Pentagon Memorial Fund.

Flags at each ballpark will be flown at half-staff, and a public service announcement about the New York museum will be aired at each stadium. Both MLB and the MLB Players Association are founding donors of the museum.

--Field Level Media

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