A $63.9 million loan from CIT Group Inc. and Square Mile Capital Management is financing development of downtown Lynn’s largest project in decades.

Saugus-based Procopio Cos. and The Carlyle Group are joint venture partners on The Caldwell, a 259-unit, 180,000-square-foot apartment tower.

“This transaction allowed us to further expand our lending portfolio in Boston by capitalizing an asset that will be well-positioned as one of the highest quality apartment buildings north of Boston with strong transit accessibility,” Mike Kusy, a vice president at Square Mile Capital, said in a statement.

Jeff Black of Colliers International’s Boston office arranged the financing for the developers.

Scheduled for completion in mid-2021, The Caldwell will contain 100 percent market-rate apartments with rents starting in the low $2,000s, developers said in January. Amenities at the 10-story tower, located next to the MBTA commuter rail station, will include a roof deck, swimming pool, fitness center and sports/gaming lounge.

Lynn city councilors rezoned portions of the downtown, including the Munroe Street parcel, in 2016 to allow 10-story buildings by right with zero setbacks and no parking requirements as part of an effort to revitalize the area.