Charles Ellicott Commentary Leviticus 16:18

"And he shall go out unto the altar that is before Jehovah, and make atonement for it, and shall take of the blood of the bullock, and of the blood of the goat, and put it upon the horns of the altar round about." — Leviticus 16:18 (ASV)

And he shall go out unto the altar. —The authorities during the Second Temple interpreted this to mean the golden altar, or the altar of incense, which stood in the Holy Place opposite the Holy of Holies, as this was the altar for which expiation was made once a year on this day ; therefore, it was cleansed next. Beginning at the northeastern corner, the high priest then went to the northwestern, then the southwestern, and finally to the southeastern corner.