and one may not build it on top of tunnels.

The Gemara relates that after reconsidering the reason for the expansion of the altar, Rav Yosef said: Is this not as it is taught in a baraita with regard to the verse: “And they set the altar upon its bases” (Ezra 3:3), which teaches that in the Second Temple the size of the altar reached its full measure, i.e., that it was the ideal size, whereas in the First Temple it was not the ideal size? The Gemara asks: But isn’t it written with regard to the instructions David gave Solomon about how to build the Temple: “All this in writing, as the Lord has made me wise by His hand upon me, even all the works of this pattern” (I Chronicles 28:19), indicating that the design of the First Temple was dictated by God?

Rather, Rav Yosef said: The size of the altar in the First Temple was ideal, but in the Second Temple era there was a need to expand the altar, and they found a verse and interpreted it as follows. The verse states: “Then David said: This is the House of the Lord God, and this is the altar of burnt offering for Israel” (I Chronicles 22:1). The verse juxtaposes the House, i.e., the Temple, with the altar, which indicates that the altar is like the Temple: Just as the House was sixty cubits (see I Kings 6:2), so too, the altar may be extended up to a length of sixty cubits.

§ The Gemara discusses the construction of the altar in the Second Temple. The Gemara asks: Granted, with regard to the location of the House, its shape was discernable from the vestiges of its foundations; but how did they know the proper location of the altar?

The Gemara answers that Rabbi Elazar says: They saw a vision of the altar already built and Michael the archangel standing and sacrificing offerings upon it. And Rabbi Yitzḥak Nappaḥa says: They saw a vision of the ashes of Isaac that were placed in that location. And Rabbi Shmuel bar Naḥmani says: From the entire House they smelled the scent of incense, yet from there, the location of the altar, they smelled a scent of burned animal limbs.

Rabba bar bar Ḥana says that Rabbi Yoḥanan says: Three prophets ascended with them from the exile: One who testified to them about the size and shape of the altar, and one who testified to them about the proper location of the altar, and one who testified to them that one sacrifices offerings even if there is no Temple, provided that there is a proper altar.

It was taught in a baraita that Rabbi Eliezer ben Yaakov says: Three prophets ascended with the Jewish people from the exile: One who testified to them about the size and shape of the altar and about the proper location of the altar, and one who testified to them that one sacrifices offerings even if there is no Temple, and one who testified to them about the Torah and instructed that it be written in Assyrian script [Ashurit] rather than the ancient Hebrew script used in the times of Moses.

§ The Sages taught in a baraita: The corner built at each point where the edges of the altar meet, the ramp upon which the priests ascended the altar, the base of the altar, and the requirement that the altar must be exactly square, are all indispensable in order for the altar to be fit for use. But the measurement of its length, and the measurement of its width, and the measurement of its height are not indispensable. The Gemara asks: From where are these matters derived? Rav Huna says: In reference to each of these characteristics the verse states the term “the altar,” and there is a principle that wherever the term “the altar” is stated, it serves to indicate that the halakhic detail mentioned is indispensable.

The Gemara asks: If that is so, then the engraving [kiyyur] that was on the altar according to Rabbi Yehuda HaNasi, or the surrounding ledge of the altar according to Rabbi Yosei, son of Rabbi Yehuda, should also be indispensable, as it is written: “And you shall put it under the karkov of the altar beneath” (Exodus 27:5). And it is taught in a baraita: What is the karkov? Rabbi Yehuda HaNasi says: This is the engraving on the altar. Rabbi Yosei, son of Rabbi Yehuda, says: This is the surrounding ledge.

The Gemara answers: Yes, the karkov is also indispensable, as it is taught in a baraita: On that day when etrogim were pelted at a Sadducee priest who poured the water libation of Sukkot on his feet rather than on the altar (see Sukka 48b), the corner of the altar was damaged as a result of the pelting and the ensuing chaos. They brought a fistful of salt and sealed the damaged section. They did this not because it rendered the altar fit for the Temple service, but in deference to the altar, so that the altar would not be seen in its damaged state. The reason the altar is disqualified is because any altar that does not have a corner, a ramp, and a base, and any altar that is not square, is disqualified. Rabbi Yosei, son of Rabbi Yehuda, says: Even the surrounding ledge is indispensable.

§ The Sages taught in a baraita: What is the karkov of the altar? It is the area between one corner and the next corner, which is the cubit-wide place on top of the altar where the priests would walk. The Gemara asks: Is that to say that the priests would walk between one corner and the next corner? The Gemara answers: Rather, say: The karkov is the cubit-wide area between one corner and the other, and there was an additional cubit that was the place where the priests would walk.

The Gemara asks: But isn’t it written: “And he made for the altar a grating of network of brass, under the karkov beneath, reaching halfway up” (Exodus 38:4), which indicates that the karkov was on the side of the altar and not on top of it? The Gemara answers: Rav Naḥman bar Yitzḥak said: There were two entities called karkov. One was a slight protrusion above the midway point of the altar for aesthetic purposes, and one was an indentation on top of the altar for the benefit of the priests, to ensure that they would not slip off the top of the altar.

It was taught in a baraita cited above that the measurement of the altar’s length, and the measurement of its width, and the measurement of its height are not indispensable. Rabbi Mani says: This is the halakha provided that one does not decrease its size so that it is smaller than the altar constructed by Moses. The Gemara asks: And how large was the altar constructed by Moses? Rav Yosef says: One cubit. Those in the study hall mocked Rav Yosef, as it is written explicitly: “Five cubits long and five cubits wide; the altar shall be square” (Exodus 27:1).

Abaye said to Rav Yosef: Perhaps the Master is speaking about the area of the arrangement of wood? Since the corners took up one cubit on each side and there was an additional cubit on each side for the priests to walk, only one cubit was left for the arrangement of wood. Rav Yosef said to Abaye: The Master, i.e., Abaye, who is a great man, knows what I mean to say. Rav Yosef read, i.e., applied, the following verse to those who mocked him: