John Gill 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)

And the king went to Gibeon to sacrifice there
About four or five miles from Jerusalem; (See Gill on 1 Kings 2:28);

for that [was] the great high place ;
not that the place itself might be higher than others that were used; but here were the tabernacle of Moses, and the altar; so that it was a more dignified place, and more sacred because of them:

a thousand burnt offerings did Solomon offer upon that altar ;
the brazen altar of burnt offerings there; not at one time, but on several days successively; though Jarchi says on one day; and which was a prodigious number, never was known the like, unless at the dedication of the temple, (1 Kings 8:63 1 Kings 8:64) .