The altar is the very heart of the Holy Temple, for all of the Divine service is centered around it: all of the daily and additional offerings, as well as the individual and congregational sacrifices. All of the major ceremonies in the Temple also take place in the vicinity of the altar: the Passover sacrifice, the bringing of the firstfruits on Shavuot, and even the rejoicing with the lulav branches on Sukkot all take place around the altar.
A Precise Location, From the Beginning of Time
The exact location of the altar is extremely precise, and has been established since time immemorial. The altar built by King David and King Solomon in the days of the First Temple, as well as the one built later in the era of the Second Temple, were both erected on the very same place: for this was the very place from which Adam, the first man, was created. The sages stated: "Man was created from the very spot which atones for him" (B'reishith Rabbah 14:6). Later, it was at this spot on Mount Moriah that Abraham bound Isaac upon the altar that he had built. Through that action, Abraham declared that this would be the place of God's Temple for all time.
The Horns and the Ramp
The altar was built as a perfect square and was quite large: itreached a height of 10 amot (app. 5 meters) and its width was 32 amot (app. 16 meters). It was constructed of two main parts: the altar itself, and the ascent ramp. Both were constructed of stones and earth. On top of the altar at its four corners, there were hollow boxes which made small protrusions or "horns." These horns measured one amah square and 5 handbreadths high, each (or, app. 18" x 18" x 15"). The Bible states that the altar may not be approached by way of steps, since this would be considered unseemly and immodest behavior for this holy place: "Do not climb up to My altar with steps, so that your nakedness not be revealed on it" (Ex. 20:23).
Three Fires Atop the Altar
Three separate piles of wood burned atop the altar. The largest of these arrangements was designated to receive all the sacrifices; the second provided the coals for the incense altar within the sanctuary, and the third was the "perpetual fire" which constantly burned on the altar, as the verse states (Lev. 6:5) "And a fire shall burn there on the altar constantly; it shall not be extinguished."
A large pile of ashes formed in the center of the altar from the remnants of these fires. God commanded that the coals be removed from here, and brought to another location outside of the Holy Temple which was known as the "place of ashes."