PHILADELPHIA — A large, impassioned crowd of Bernie Sanders supporters — chanting “Hell, no, D.N.C., we won’t vote for Hillary” — marched on Sunday afternoon to the site of the Democratic National Convention, promising a week in which the party’s divisions will be on vivid display in the streets.

More than 1,000 people from as far as Seattle and Florida participated in the first of what are expected to be many Sanders rallies during the convention, which formally begins Monday. The march, led by a banner proclaiming “Help End Establishment Politics, Vote No on Hillary,” was far larger than any of the protest marches last week in Cleveland at the Republican National Convention.

Despite the size of the demonstration, it was a peaceful assembly with no signs of supporters of Donald J. Trump, the Republican nominee, and the police maintained a low-key, even casual presence. Marchers headed down Broad Street past fire hydrants spraying cooling jets in the sweltering 97-degree heat.