descend upon

verb4

1. •
   To arrive, usually without warning or invitation.
2. •
   To arrive suddenly or unexpectedly, especially in a manner that causes disruption or inconvenience.

   • My neighbour descended upon me just as I was walking out the door.
3. •
   To visit in large numbers, especially a public place.

   • This fall, millions of devout Muslims will descend upon Mecca, Medina, and Saudi Arabia's holy sites in one of the largest annual migrations in human history. — 2013
4. •
   To make an attack or incursion, from or as if from a vantage ground; to come suddenly and with violence.