As support for the Vermont Democrat grows, hundreds got together in Boston on the greenway outside South Station Tuesday night to rally for Bernie Sanders, candidate for president.

Sanders, an underdog candidate trailing far behind Democratic frontrunner Hillary Clinton, has seen his stock rise among liberal voters in recent weeks. Rallies have swollen in size beyond expectations.

The same was true in Boston. The city’s grassroots organizing kick-off was originally scheduled to be held in Encuentro 5, a space downtown, said organizer Ed Schluessel. When it gained traction on Facebook, he said, the event moved to Dewey Square.

“The fact is people are hungry for some kind of political alternative in this country,” Schluessel said. “The idea of a movement is resonating and very prominent.”

Sanders was not at the rally. Putting on the event cost just a few hundred dollars for rental audio equipment, Schluessel said.

Sanders is polling more than 30 points behind Clinton among Democrats, according to a recent Monmouth University poll.