It has the article: the strong man. So Rev. See on Mat 12:29.
Armed (καθωπλισμένος)
Fully armed: down (κατά) from head to heel.
His palace (ἑαυτοῦ αὐλήν)
Lit., his own. Ἀυλή is strictly the open court in front of a house: later, the court round which the house is built, and so applied to the house generally, as our door or roof. Rev., court; for there, in the open space, commanding the doors, he would mount guard.