Albert Barnes Commentary 1 Kings 3:4

"And the king went to Gibeon to sacrifice there; for that was the great high place: a thousand burnt-offerings did Solomon offer upon that altar." — 1 Kings 3:4 (ASV)

Gibeon - The transfer to Gibeon of the “tabernacle of the congregation” and the bronze “altar of burnt offerings” made by Moses, which were removed there from Nob (Compare 1 Samuel 21:6 and its marginal notes), had made it “the great high-place”—that is, more sacred than any other in the holy land, unless it was Mount Zion, where the ark had been brought by David. For the location of Gibeon, see the note on Joshua 9:3.

A thousand burnt offerings did Solomon offer. He presented the victims, while the priests were the actual sacrificers (1 Kings 8:5). A sacrifice of a thousand victims was an act of royal magnificence suited to the greatness of Solomon. In the same way, Xerxes offered 1,000 oxen at Troy. If the offerings in this case were “whole burnt offerings” and were all offered on the altar of Moses, the sacrifice must have lasted several days.