'Altar' in the Bible

When He opened the fifth seal, I saw under the altar the people slaughtered because of God’s word and the testimony they had.

Another angel, with a gold incense burner, came and stood at the altar. He was given a large amount of incense to offer with the prayers of all the saints on the gold altar in front of the throne.

The angel took the incense burner, filled it with fire from the altar, and hurled it to the earth; there were rumblings of thunder, flashes of lightning, and an earthquake.

The sixth angel blew his trumpet. From the four horns of the gold altar that is before God, I heard a voice

Then I was given a measuring reed like a rod, with these words: “Go and measure God’s sanctuary and the altar, and count those who worship there.

Yet another angel, who had authority over fire, came from the altar, and he called with a loud voice to the one who had the sharp sickle, “Use your sharp sickle and gather the clusters of grapes from earth’s vineyard, because its grapes have ripened.”

Then I heard someone from the altar say:Yes, Lord God, the Almighty,true and righteous are Your judgments.