Developers, investors and city officials formally introduced USQ, a 15-acre, $2B life sciences and residential project in Somerville’s Union Square, in a groundbreaking ceremony Wednesday.

Officials from Magellan Development, RAS Development, Cypress Equity Investments and USAA Real Estate turned some dirt to usher in the initial phase of USQ before a crowd in a tent atop the active construction site.

The developers plan to deliver 194K SF of life sciences space and 450 apartment units to the site by spring 2023. The project sits next to the incoming Union Square Station on the MBTA Green Line, part of a larger extension expected to serve riders by December.

“We were all attracted to the city’s vision,” Greg Karczewski, a partner at RAS and the development lead for USQ, said to reporters after the event. “A great workforce population and a mile away from the most innovative square mile in the world, it was an easy decision to put our time, energy and capital into Union Square.”

The plot sits at the southeastern corner of Somerville Avenue and Prospect Street, 2 miles from Cambridge’s Kendall Square and steps from Union Square Plaza, which is home to restaurants, retail and entertainment spaces.

USQ's first phase includes 10 Prospect St., a seven-story life sciences building expected to be completed in winter 2022, and 20-50 Prospect St., which includes adjacent 25-story and six-story residential towers totaling 450 apartment units, 90 of which will be designated as affordable.

The project broke ground seven years after the joint venture, operating as an entity dubbed US2, secured the development rights for the site. The Somerville Board of Aldermen approved zoning relief for USQ in 2017, and the joint venture earlier this year secured $239M in financing from Bank OZK for the project’s first phase.

Architecture firm SGA and Gilbane Building Co. are behind 10 Prospect St.; architects Höweler & Yoon, bKL Architecture and Cranshaw Construction are building 20-50 Prospect St. JLL is leasing the life sciences tower, while Boston-based Graffito SP leads retail leasing efforts.

The developers plan to deliver 2.4M SF of mixed-use development and 1.2M SF of lab and office space total in the project. The site is expected to include 3.6 acres of park and public space, 140K SF of retail, 175 hotel rooms and 1,000 residences.

“We believe that we’re addressing what is a significant shortage of housing,” USAA Real Estate President and CEO Len O’Donnell said during the event. “To do that on a rail station such as this and to enable mobility, and to be able to contribute toward creating greater housing stock in this community, is a great way to bring together that investment team.”

Somerville's population of 81,000 residents spans 4.1 square miles, making it one of the most densely populated cities in New England, Somerville Mayor Joseph Curtatone said. Minutes from Cambridge and Boston, the city hasn’t seen the pace of life sciences investment as some of Boston’s other suburbs.

Union Square was an economic hub in the early 1900s with busy streetcar and passenger train stations, but activity waned in the late century following flight to the suburbs and highway development, according to a Somerville neighborhood profile.

“This development is crucial,” Curtatone said. “We deemed a long time ago we needed control of our financial destiny.”

The project is Somerville’s second significant life sciences development, after the 1.3M SF Boynton Yards project by DLJ Real Estate Capital Partners and Leggat McCall Properties. That partnership secured 208K SF of combined leases from Flagship Pioneering at its first building, 101 South St.

Karczewski said the development team is a cheerleader for 101 South St., and he hopes the projects combine to create a new life sciences cluster. Life sciences tenants both small and large have already expressed interest in 10 Prospect St., he added.

“The more vibrancy that we can create around the life sciences community right in the heart of the square only serves to help continue our efforts to create this into an urban employment district,” Karczewski said.