Smith's Bible Dictionary
Altar. The first altar of which we have any account is that built by Noah when he left the ark. Genesis 8:20. In the early times, altars were usually built in certain spots hallowed by religious associations, for example, where God appeared. Genesis 12:7; Genesis 13:18; Genesis 26:25; Genesis 35:1. Though generally erected for the offering of sacrifice, in some instances, they appear to have been only memorials. Genesis 12:7; Exodus 17:15-16. Altars were most probably originally made of earth. The law of Moses allowed them to be made of either earth or unhewn stones. Exodus 20:24-25.
I. The Altar of Burnt Offering. It differed in construction at different times.
(1) In the Tabernacle, Exodus 27:1 ff.; Exodus 38:1 ff., it was comparatively small and portable. In shape it was square. It as five cubits in length, the same in breadth, and three cubits high. It was made of planks of shittim (or acacia) wood overlaid with brass. The interior was hollow. Exodus 27:8. At the four corners were four projections called horns made, like the altar itself, of shittim wood overlaid with brass, Exodus 27:2, and to them the victim was bound when about to be sacrificed. Psalms 118:27.
Round the altar, midway between the top and bottom, ran a projecting ledge, on which perhaps the priest stood when officiating. To the outer edge of this, again, a grating or network of brass was affixed, and reached to the bottom of the altar. At the four corners of the network were four brazen rings, into which were inserted the staves by which the altar was carried. These staves were of the same material as the altar itself. As the priests were forbidden to ascend the altar by steps, Exodus 20:26, it has been conjectured that a slope of earth led gradually up to the ledge from which they officiated. The place of the altar was at the door of the Tabernacle of the congregation). Exodus 40:29.
(2) In Solomon's Temple, the altar was considerably larger in its dimensions. It differed too in the material of which it was made, being entirely of brass. 1 Kings 8:64; 2 Chronicles 7:7. It had no grating, and instead of a single gradual slope, the ascent to it was probably made by three successive platforms, to each of which it has been supposed that steps led. The altar erected by Herod in front of the Temple was 15 cubits in height and 50 cubits in length and breadth. According to Leviticus 6:12-13, a perpetual fire was to be kept burning on the altar.
II. The Altar of Incense, called also the golden altar to distinguish it from the Altar of Burnt Offering which was called the brazen altar. Exodus 38:30.
(a) That in the Tabernacle was made of acacia wood, overlaid with pure gold. In shape it was square, being a cubit in length and breadth and two cubits in height. Like the Altar of Burnt Offering, it had horns at the four corners, which were of one piece with the rest of the altar. This altar stood in the Holy Place, "before the vail that is by the Ark of the Testimony." Exodus 30:6; Exodus 40:5.
(b) The altar of Solomon's Temple was similar, 1 Kings 7:48; 1 Chronicles 28:18, but was made of cedar overlaid with gold.
III. Other Altars. In Acts 17:23, reference is made to an alter to an unknown God. There were several altars in Athens with this inscription, erected during the time of a plague. Since they knew not what god was offended and required to be propitiated.
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Smith, William, Dr. Entry for 'Altar'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/a/altar.html. 1901.