In the Genesis account of Noah’s Ark, Noah built an altar after leaving the vessel. Genesis 8:20 says that he constructed the altar and offered burnt offerings from selected clean animals and birds.
The act follows the Ark’s grounding, the drying of the earth, and God’s command for Noah and the animals to leave. Noah’s first recorded construction after the flood is therefore a place of worship, not a new home or a tower.
The passage also introduces a distinction between clean and unclean animals. Genesis says Noah took additional clean animals and birds into the Ark, while the later offering uses some of them. This detail is separate from the broad summary that animals entered the Ark in pairs.
The altar scene leads directly into God’s post-flood covenant with Noah. The rainbow is then given as the covenant sign, a detail often remembered more strongly than the altar that precedes it.