Marius is a lunar crater located on the Oceanus Procellarum. The surface to the west and north of this crater contains a large number of lunar domes spread across an area over a hundred kilometers in diameter that may be of volcanic origin dubbed the Marius Hills. These domes, if volcanic, may have been formed by magma that is fairly more viscous than the volcanic material that formed the basaltic lunar maria. The nearest named crater feature is Reiner to the southwest. Kepler is located to the east-southeast, and rays from that formation reach the rim of Marius.