Jamieson, Fausset and Brown on Mark 5:13

13. And forthwith Jesus gave them leave--In Matthew (Mt 8:32) this is given with majestic brevity--"Go!" The owners, if Jews, drove an illegal trade; if heathens, they insulted the national religion: in either case the permission was just.

And the unclean spirits went out--of the man.

and entered into the swine: and the herd ran violently--rushed.

down a steep place--down the hanging cliff.

into the sea (they were about two thousand)--The number of them is given by this graphic Evangelist alone.

and were choked in the sea--"perished in the waters" (Mt 8:32).