descend upon (something)

1. Literally, to drop onto someone or something. No one was too pleased when rain began to descend upon our picnic. Bits of debris from the explosion descended upon the town below. Mom knew we were having a pillow fight in the upstairs hallway when feathers began to descend upon her.

2. By extension, to converge at a particular place or thing, often in great numbers. The kids descended upon the birthday cake like locusts. Thousands of people descend upon the town each year to attend the video game conference. Shoppers descended upon our wares as soon as we opened the doors on Black Friday.