1 Kings 1:50 - Matthew Poole's English Annotations on the Holy Bible

Either that which was at Gibeon, as appears from 1 Chronicles 16:39 2 Chronicles 1:3; and was made with four horns, Exodus 38:2; to which the sacrifices were bound Psalms 118:27. Or rather, that which set David had lately up in the threshing-floor of Araunah, which doubtless was made after the same form as that at Gibeon; for, first, This was next at hand. Secondly, The altar only is mentioned here, whereas in Joab's case there is mention of the tabernacle and altar both, 1 Kings 2:28,29, which seems to be noted to distinguish the two altars; for Adonijah being the king's son, he might safely go to Araunah's altar, and the people would not be forward to seize upon him, or bring him to justice: but Joab truly thought it was not safe for him to venture himself there, and therefore he fleeth to Gibeon, as a place more remote from Jerusalem. Hither he fled, either to implore God's mercy; or rather, to avoid Solomon's rage; supposing that his reverence to that sacred place would not permit him to pollute it with his brother's blood; or that the consideration of God's grace and mercy, which himself needed and begged of God, in pardoning his offences, and accepting the sacrifices which he should offer there, would engage and dispose him to show mercy to his offending and now penitent brother; or that his piety would not allow him violently to pluck him as it were out of the arms of God, into which he had put himself. And for these or such-like reasons the altar was esteemed a kind of sanctuary or place of refuge, not only among the Gentiles, but also among the Hebrews, though it be not called by that name, as may be gathered from Exodus 21:14 1 Kings 2:28.