1 Kings 1:50

caught hold on the horns of the altar In his terror Adonijah takes sanctuary, apparently at the altar which had been erected when the ark was brought to Mt. Zion. That an altar was set up there is clear from 2 Samuel 6:17-18, where we have an account of the burnt offerings and peace offerings presented there. As this sanctuary was specially under the care of Abiathar, it was natural that Adonijah should go there. It may have been by Abiathar's advice.

The horns of the altar are described Exodus 27:2 seqq. They were wooden projections overlaid with brass. On the occasion of a sacrifice the priest with his finger was to smear them with the blood of the victim (Exodus 29:12), and this ceremonial was a sign of atonement (Exodus 30:10). Thus the spot to which Adonijah fled was of special sanctity.