Albert Barnes Commentary 2 Kings 9:13

"Then they hasted, and took every man his garment, and put it under him on the top of the stairs, and blew the trumpet, saying, Jehu is king." — 2 Kings 9:13 (ASV)

Took every man his garment, and put it under him - The outer cloak of the Jews was a type of large shawl or blanket, which could serve as a carpet of state. Such a carpet is commonly depicted on the seat of an Assyrian throne in the Nineveh sculptures.

The stairs rose against the wall of the house from the pavement of the court to the level of the upper story or the roof. At the top of the stairs would be a flat platform, which would serve as a throne where the new king could present himself to his subjects.

Blew with trumpets - This was a recognized part of the coronation ceremony (see 2 Kings 11:14; 2 Samuel 15:10; 1 Kings 1:39).