A history of the Green Line extension to Somerville

The Green Line project calls for service to extend north from Lechmere, the current terminus. –Barry Chin/Globe Staff/File

News that the MBTA had terminated its contract with the engineering firm overseeing the construction of the Green Line extension project represented the latest step in its decades-long history.

As with any subway, the path for the $2.3 billion project has been paved with starts, stops, and turns. Overall, it’s been a bumpy ride.

To get you up to speed, here’s a look back at some key events during the project, which would feature six new stops and is scheduled for completion in 2021.