The West Bath is the earliest example of the seven public baths found within the ruins of Jerash. They are thought to have been built in the early 2nd century, but they have not yet been excavated and it is entirely possible that they could date to the end of the 1st century. The baths are typically Roman in style, with the bathing rooms sitting at the center of a large court enclosed by porticoes. This was known as a palaestra, a recreation area where bathers gathered before or after and which was possibly used for sports. The baths themselves were made up of several rooms for hot, warm and cold bathing.

Originally a three room complex, the baths were enlarged in the 3rd century on a perfectly symmetrical (imperial) plan. A remarkable feature of this structure is the large system of vaults that covered the bathing rooms, in particular the cupolas. While concrete cupolas were often standard roofing for Roman baths, the West Bath cupolas were constructed from stone and were remarkably strong. One of these has survived the centuries and been perfectly conserved till today. It is the earliest known structure of this type still in situ in the world.