I want to know the answer to the following question:
A train full of gravel came from Needham to fill what?
All the background I'm provided with is that "The geography of downtown and South Boston was particularly impacted by the Central Artery/Tunnel Project (known unofficially as the "Big Dig"), which allowed for the removal of the unsightly elevated Central Artery and the incorporation of new green spaces and open areas.". Is that enough to answer the question?