Northeastern celebrated a significant milestone on Friday afternoon in the construction of GrandMarc, the university’s newest residence hall, as the final steel beam was added to the structure.

GrandMarc is a 17-story building under construction behind the YMCA of Greater Boston by Phoenix Property Company and Suffolk Construction. The project will add 720 beds in on-campus housing for both first-year students and upperclassmen. Construction began in August 2012, and the building is expected to open during the next academic year in January 2015.

President Joseph E. Aoun welcomed Boston Mayor Thomas Menino, Massachusetts Rep. Jeffrey Sanchez, and Boston City Councilor Michael Ross at Friday’s topping-off ceremony, held on St. Botolph Street. Many people affiliated with the project, including the construction crews, Aoun, and Menino, signed the white beam before it was ceremoniously raised and put in place.

In his remarks, Aoun thanked Menino for his leadership and support on the project and presented him with a brick from the former gymnasium where GrandMarc now stands.

“This is an emotional moment for us,” Aoun told those gathered at the event. “This is really a collective effort. But without the mayor, we would not be here today. We would not have a building. He made it happen.”

Under the innovative agreement between Northeastern, Phoenix Property, and the YMCA, Phoenix purchased the land on St. Botolph Street from the YMCA and invested $75 million to build GrandMarc. Northeastern will lease the building from Phoenix, with the opportunity to purchase it in the future. This is the first time in the city’s history a third party is developing a college dormitory.

Topping-off ceremonies date back to about 2,700 B.C. when the first stone building in Egypt was completed. Today in the United States, the ceremony celebrates crews reaching the highest component of a project, instead of the completion of a project.

In addition to signatures, the beam was adorned with a small evergreen tree and the American flag, which recognizes the success and hard work of America’s tradespeople.

It was in 1898 when Northeastern held its first class at the YMCA, and Aoun noted the university is coming full circle by building a residence hall right next to its former home.

Menino said GrandMarc is not just a positive for Northeastern, but also for the city as it will free up private residences in neighborhoods that surround the campus where students live.

“This is a very special day,” Menino said. “Every dormitory bed we create puts four private apartments back on the streets, and that is important. The only reason this was successful is because of people working together. This is a good project for the university, the city, and the neighborhood.”

During his remarks, Mark DiNapoli, president and general manager of Suffolk Construction, also recognized two Northeastern civil engineering co-op students— Katie Doherty and Nick Pettingill—who have worked at the site.