On the “horns” of the altar, see Exodus 27:2 note. The altar to which Adonijah fled was probably in the “tabernacle” already referred to 1 Kings 1:39.
Related Commentaries of 1 Kings 1:50
1 Kings 1:50
50 And Adonijah feared because of Solomon, and arose, and went, and caught hold on the horns of the altar.