Courtesy of WBZ

Construction crews unearthed the remains of a 19th-century shipwreck buried beneath the 121 Seaport building site in Boston, prompting an impromptu archaeological dig in the heart of the neighborhood’s bustling building activity.

City archaeologist Joe Bagley told WBZ-TV that it’s believed to be the first shipwreck discovered in Boston on filled land.

The 50-foot wooden sloop was discovered last week approximately 25 feet below grade as construction crews continue site work for an underground parking garage and foundation elements for a 425,000 square foot office tower. Workers also found barrels of lime that apparently were part of the ship’s cargo, and notified city officials of the unusual find. Developer Skanska USA temporarily halted construction to allow Bagley and other researchers to bring in additional imaging equipment this week.

Mud flats stretched over portions of the modern-day Seaport District before being filled in during the 19th century to make way for warehouses and rail yards to support the shipping trade. More recently, the MBTA Silver Line tunnel was built under 121 Seaport and nearby parcels where large residential projects are planned.

Skanska broke ground last July on the 1-acre site at the corner of Seaport Boulevard and Boston Wharf Road. CBT Architects designed an 18-story tower including offices and a two-story retail podium. Skanska is building the project on speculation.

Skanska USA Civil Northeast, the Swedish developer’s civil engineering arm, is overseeing the project using an “up-down” construction process involving simultaneous work on the foundation and the building superstructure.