1. Amos 9:1 (ESV)
  2. Exposition

Which altar is being referred to?

Amos 9:1 (ESV)

1 I saw the Lord standing beside the altar, and he said: “Strike the capitals until the thresholds shake, and shatter them on the heads of all the people; and those who are left of them I will kill with the sword; not one of them shall flee away; not one of them shall escape.

The location of the altar is unspecified. It may have been the shrine at Bethel since that was prominent in Amos 7:1–17. It could also have been at Dan or maybe Beersheba.1