Apollinaris Mons is an ancient shield volcano in the southern hemisphere of Mars.

It is situated near the equator, south of Elysium Planitia and north of the impact crater Gusev (the landing site of the Mars rover Spirit).

[3][better source needed] On the top of this volcano is a caldera about 80 km (50 miles) in diameter.

[6] Apollinaris Patera parallels many of the volcanic terrains on Mars, including most of the Elysium and Tharsis Rises, in that they are demagnetized terrains that conspicuously predate the shutdown of the Martian dynamo.

Researchers observing this noted that the deposition of lavas atop an older, more magnetized terrain might have led to the region's demagnetization.