1.
If the police or army ~ a number of people, they arrest or capture them.
The police rounded up a number of suspects...
She says the patrolmen rounded them up at the village school and beat them with rifle butts.
PHRASAL VERB: V P n (not pron), V n P
2.
If you ~ animals or things, you gather them together.
He had sought work as a cowboy, rounding up cattle...
PHRASAL VERB: V P n (not pron)
3.
see also round 2, roundup