Please give us some context: Where did you see the sentence? Who were the people? Were the people differently shaped, or were the shapes something else? Upward from where? It's very hard to imagine what may be happening without answers to these questions.
The sentence comes from Martin Amis's latest novel "Lionel Asbo", describing how Diston Town, a crime-ridden place, was like. The preceding sentence is: "But it would be foolish to suppose that each and every gangbanger and posse-artist (and every Yardie and jihadi) in the entire manor had heard tell of the great asocial."
Can you give us a couple of sentences after the sentence in question? This is an unusual sentence, in my experience.
 I found the text on Google Books. The only guess I have is that it is a different way to "rose up". Different types of people appeared on the streets at night compared to the ones you saw in daylight.