The horns of the altar were the place of mercy:
“The laying hold upon the literal horns of an altar, which can be handled, availed not Joab. There are many—oh, how many still!—that are hoping to be saved, because they lay hold, as they think, upon the horns of the sacraments. Men of unhallowed life, nevertheless, come to the sacramental table, looking for a blessing. Do they not know that they pollute it? Do they not know that they are committing a high sin, and a great misdemeanor against God, by coming amongst his people, where they have no right to be? And yet they think that by committing this atrocity they are securing to themselves safety. How common it is to find in this city, when an irreligious man is dying, that someone will say, ‘Oh, he is all right; for a clergyman has been, and given him the sacrament.’ I often marvel how men calling themselves the servants of God can dare thus to profane the ordinance of the Lord. Did he ever intend the blessed memorial of the Lord’s supper to be a kind of superstitious vialicum, a something upon which ungodly men may depend in their last hour, as if it could put away sin.” Charles Spurgeon
1 Kings 1:50 Now Adonijah was afraid of Solomon; so he arose, and went and took hold of the horns of the altar.51 And it was told Solomon, saying, Indeed Adonijah is afraid of King Solomon; for look, he has taken hold of the horns of the altar, saying, Let King Solomon swear to me today that he will not put his servant to death with the sword.