According to Genesis, God gave Noah instructions for building the ark.
But in fact, the myth of the global flood that destroys all life only begins to appear in the Old Babylonian period (20th–16th centuries BCE).
The reasons for this emergence of the typical Mesopotamian flood myth may have been bound up with the specific circumstances of the end of the Third Dynasty of Ur around 2004 BCE and the restoration of order by the First Dynasty of Isin.
The last known version of the Mesopotamian flood story was written in Greek in the 3rd century BCE by a Babylonian priest named Berossus.
From the fragments that survive, it seems little changed from the versions of two thousand years before.
(The word for the ark of the covenant Noah is warned of the coming flood and told to construct the ark.
God spells out to Noah the dimensions of the vessel: 300 cubits in length, 50 cubits in width and 30 cubits in height (450 × 75 × 45 ft or 137 × 22.9 × 13.7 m).The story goes on to describe the ark being afloat for 150 days and then coming to rest on the Mountains of Ararat and the subsequent receding of the waters. "Noah's boat").The Genesis flood narrative is similar to numerous other flood myths from a variety of cultures.This remains the basic plot for several subsequent flood-stories and heroes, including Noah. In Babylonian versions his name is Atrahasis, but the meaning is the same.In the Atrahasis version, the flood is a river flood.In the Babylonian Epic of Gilgamesh the reasons are not given and the flood appears to be the result of the caprice of the gods.