On the eve of their national convention, the president of Delta Sigma Theta Sorority and other national leaders took part in a reception at the Oxon Hill Mansion, in Oxon Hill, Md. on July 9. (Hamil Harris/The Washington Post)

The Deltas stood in an elegant line of crimson and cream on the steps of Oxon Hill Manor on Tuesday night, awaiting the arrival of their ailing sister, Christa Beverly Baker, the first lady of Prince George’s County.

Inside the mansion, servers hurried to arrange vases of red roses, pass trays of strawberries and melted chocolate, and set out glasses for punch. The evening would be a fine celebration of black sisterhood, a 100-year tradition of being there for women through the good and the bad. If you belong to Delta Sigma Theta sorority, they say, there is little need to say more.

When Baker emerged from a black SUV, escorted by her husband, County Executive Rushern L. Baker III (D), the Deltas embraced her. Christa Baker, 53, who received a diagnosis of Alzheimer’s disease three years ago, smiled in recognition of the sorority that she has loved since she was a student at Howard University. The Deltas took her hand and led her up the steps of the mansion into the reception.

Under a white tent on the lawn of the mansion that overlooks the Potomac, Rushern Baker thanked the Deltas for their visits and support as he runs one of the country’s wealthiest majority-minority counties and cares for his wife of 27 years.

The women who pledged the sorority at the same time as Christa Baker — together they were known as the “indomitable 21” — have cooked for her in her home or stopped by with meals. They’ve taken her on outings and sat with her for hours.

Delta Sigma Theta centennial chair Gwendolyn Boyd talks about the sorority’s convention events. (Hamil R. Harris/The Washington Post)

“When the rock of our life, the person who holds us together, the person who did it all needed help — as soon as that went out, members of Delta Sigma Theta not only wrapped their arms around her, but they wrapped their arms around all of us, and they have not stopped wrapping their arms around us,” Baker said. “My wife loves Delta Sigma Theta. If you don’t believe it, ask one of my children. We see so much red we don’t know what to do.”

The Oxon Hill Manor reception was the first of dozens of celebrations planned this week as part of Delta Sigma Theta’s 51st national convention, which officially kicks off Friday with a lighting of the Delta Torch on the Mall, where 60,000 red-clad Deltas are expected to convene. The week-long convention includes a health walk, leadership academies, a step show Friday night at the Verizon Center, an ecumenical Sunday church service, luncheons, a gospel concert and a dedication of the first stained-glass window featuring African American women at Howard University’s Rankin Chapel.

“We are celebrating 100 years of sisterhood, 100 years of fighting for women’s rights, 100 years of fighting for civil rights,” said Cynthia Butler-McIntyre, national president of Delta Sigma Theta, which operates on the theme: “A sisterhood called to serve.”

Delta Sigma Theta was founded on Jan. 13, 1913, by 22 women at Howard University, who had decided to break away from the sorority Alpha Kappa Alpha and create a new organization focused on academic excellence and community service. In March of that year, the founders’ first act of service was to join the women’s suffrage march on Washington.

“We are still here 100 years later doing what the 22 called us to do,” Butler-McIntyre said.

The centennial commemoration of the sorority’s founding began in January with a procession in the Tournament of Roses Parade in Pasadena, Calif.; a lighting of a Delta Torch that passed through 22 cities; and a reenactment of the women’s suffrage march.

“Delta not only celebrates history, we make history,” said Gwendolyn Elizabeth Boyd, an engineer and past national president of the Deltas. “Any organization that turns 100 and remains on mission, that is significant. . . . Being a sisterhood called to serve, we are all connected by a common purpose to give back — to make sure we leave the world better than we found it.

Well-known Deltas include: Betty Shabazz, the widow of Malcolm X; civil rights icon Fannie Lou Hamer; human rights activist Mary McLeod Bethune; actress Ruby Dee; singers Roberta Flack, Aretha Franklin and Lena Horne; and congresswomen Shirley Chisholm and Barbara Jordan.

When Deltas say they are an organization dedicated to service, Butler-McIntyre said, “we are not boasting and bragging. We are just giving facts.”

In Prince George’s County, which has the largest chapter of the Deltas in the world, members include educators, legislators, judges and lawyers.

“We are glad to celebrate, but we still have a lot to do and the mission is clear: service, sisterhood and scholarship,” Prince George’s State’s Attorney Angela D. Alsobrooks said. “All of us are together in terms of our priority. . . . I am really moved by our first lady Christa Beverly. She is the reason we are here tonight.”

Butler-McIntyre told the crowd that the Deltas had received many invitations to attend receptions celebrating their anniversary. But, she said, the invitation from Prince George’s, which is lobbying to host the Deltas’ 2014 convention, took priority.

“Somebody called and said Brother Baker is married to a Delta,” McIntyre said, turning to the county executive who sat at a table with Christa Baker and their three children. “You need to thank soror Baker for us being here tonight. That’s how you got bumped up on the list.”

Throughout the evening, the Deltas explained sisterhood, a bond that allows a woman to skip over long introductions provides almost instant familiarity and trust.

Artis Hampshire-Cowan, a Howard University administrator who lives in Mitchellville, recalled a time years ago when she was traveling down a highway in Alabama. Running low on gas and money, she decided to pull off the highway at Alabama State University. On campus she looked for Deltas and didn’t even have to explain why she had no money. They reached into pocketbooks to put gas in her tank.

“That sisterhood is immediate,” Hampshire-Cowan said. “When you say you are a Delta to another Delta, it allows you to skip over” formalities. “That is sisterhood. No matter where you go, you have family.”

“Sisterhood means standing together in collective action,” said Vashti Murphy McKenzie, the first woman elected bishop in the history of the African Methodist Episcopal Church. “Like tonight, the first lady of the county, we stand with her. We stand with each other in good times and challenging times.”

The sorors lined up to take photos with Christa Baker, who clutched a bouquet of flowers wrapped in a crimson ribbon.