Walk through Amos, verse by verse, with the great Bible Commentaries of Matthew Henry (1662 - 1714) & Adam Clarke (1760 - 1832)
3:9
Publish in the palaces at Ashdod, and in the palaces in the land of Egypt, and say, Assemble yourselves upon the mountains of Samaria, and behold the great tumults in the midst thereof, and the oppressed in the midst thereof. KJV
{Make ye heard in the houses of Ashdod, and in the houses of the land of Egypt; and say ye, Be ye gathered together on the hills of Samaria, and see ye many strong vengeances in the midst thereof, and them that suffer false challenge in the privy places thereof.} Wycliffe's Bible
Publish in the palaces - The housetops or flat roofs were the places from which public declarations were made.
The prophet is ordered to publish it in the palaces of Ashdod, one of the chief cities of the philistines; nay, the summons must go further, even to the palaces in the land of Egypt. “The great men of both those nations, that dwell in the palaces, that are inquisitive concerning the affairs of the neighboring nations, and are conversant with the public intelligence, let them assemble themselves upon the mountains of Samaria,” v. 9. There, upon a throne high and lifted up, the judgment is set. Samaria is the criminal that is to be tried; let them be present at the trial, for it shall be (as other trials are) public, in the face of the country; let them make an appointment to meet there from all parts, to judge between God and his vineyard.