So much has changed in 15 years, but these four words remain a constant truth:
"We Shall Not Forget."
Sunday marks another important remembrance of what happened on Sept. 11, 2001, when al-Qaida terrorists hijacked four airliners and killed nearly 3,000 people at the World Trade Center in New York, the Pentagon in Washington and near Shanksville, Pa.
Major League Baseball, which was instrumental in helping a nation begin to heal back then, announced plans on Thursday for the league-wide commemoration, with tributes at all 15 ballparks hosting games on Sunday. This remembrance is part of MLB's ongoing effort to honor those whose lives were lost and affected on that day.

On-field personnel -- including players, coaches and umpires -- will wear caps with a side patch of an American flag during games. The Toronto Blue Jays will wear customized caps recognizing both the U.S. and Canada. MLB proceeds from sales of these caps will be donated to the 9/11 Memorial and Museum, the Pentagon Memorial and the Flight 93 Memorial.
Home clubs will mark the date with pregame ceremonies, including a moment of silence, and the "We Shall Not Forget" MLB silhouetted batter ribbon will be displayed throughout ballparks. Additionally, special lineup cards and base jewels will be used for every game played.
As it reads on the 911memorial.org website: "Despite the passing years since September 11, 2001, it remains as important as ever that we continue to come together to remember and honor the victims and our shared history."
Five years ago, when the Mets hosted the Cubs in the ESPN Sunday Night Baseball game, it was Mike Piazza -- whose emotional go-ahead homer against the Braves had highlighted the first post-9/11 game played in New York City -- leading a procession of 204 first responders onto the field for the ceremonial first pitch. For this Sunday remembrance, players from the Mets and Braves will wear New York City-based first responder caps during batting practice and during the national anthem at Turner Field.

The Nationals will host the final game of the 2016 Patriotic Series by wrapping up their series with the Phillies on Heroes Day there. Rescue, aid, military and law enforcement workers who serve our country every day will be honored as part of the observance, which will also include a variety of patriotic elements with special guests in attendance. Pregame ceremonies are dedicated to first responders and military, and it will recognize the efforts of the Pentagon Memorial Fund.
At that game, the U.S. Naval Academy Color Guard will present the colors, and more than 1,000 U.S. Naval Academy midshipmen and more than 100 first responders from the D.C., Maryland and Virginia region will line the field for the national anthem performance by more than 150 members of the U.S. Naval Academy Men's and Women's Glee Clubs and Gospel Choir. The ceremonial first pitch will be thrown by Navy Secretary Ray Mabus. The D.C. Fire Department Emerald Society Pipes & Drums will perform "God Bless America." There will also be a flyover from the VFA-103 Jolly Rogers and VFA-11 Red Rippers of Naval Air Station Oceana.
The first scheduled pitch on Sunday is at 1:05 p.m. ET at Yankee Stadium, next door to the site where the Yankees and the D-backs played unforgettable World Series games in 2001. There will be home-plate ceremonies for Simon Wiesenthal Center Heroes for Tolerance Honorees for 2016, and for wounded service men and women from Walter Reed and Fort Belvoir. The NYPD Pipes and Drums will march in playing "America the Beautiful" and "The Armed Forces Medley" and the color guard will be from the Port Authority Police Department. A giant flag will be unfurled in the outfield, and the national anthem will be sung by FDNY firefighter Frank Pizzaro.
The Red Sox, the American Red Cross, and Beth Israel Deaconess Medical Center will host the 14th annual Day of Remembrance Blood Drive at Fenway Park from 7:30 a.m. to 2:30 p.m. ET on Sunday. Those who are eligible are asked to donate blood in honor of those lost. Appointments to donate blood can be made by calling 1-800-RED CROSS or by visiting redcrossblood.org.
Those interested in donating blood can enter the ballpark through Gate D located on the corner of Yawkey Way and Van Ness Street. A blood donor card or driver's license, or two other forms of identification, are required at check-in. Individuals who are 17 years of age (16 with parental permission in some states), weigh at least 110 pounds and are in generally good health may be eligible to donate blood. High school students and other donors 18 years of age and younger also have to meet certain additional height and weight requirements.
The ESPN Sunday Night Baseball game will feature the Cubs at Astros.
In St. Louis, the Cardinals will host the Brewers -- in the same town where the late Hall of Fame broadcaster Jack Buck, in the first game there after the post-9/11 hiatus, finished his poem with these words:
Everyone is saying the same thing,
and praying that we end these senseless moments we are living.
As our fathers did before, we shall win this unwanted war.
as our children will enjoy the future we'll be giving.
Beginning Friday on MLB Network, a video narrated by retired FDNY battalion chief Vin Mavaro will look back at how 2016 Hall of Fame inductees Ken Griffey Jr. and Piazza played an important role in helping two families of FDNY firefighters heal following the tragic events of 9/11.
MLB.com and MLBCommunity.org will provide complete coverage of the day's ceremonies and perspectives through columns, news articles, multimedia and photos across the Majors. MLB Network will feature coverage and commemorate the day's events with studio programming.