The Late Paleozoic (300 Ma) archives the longest glaciation of the Phanerozoic, and Earth’s only example of icehouse collapse on a vegetated planet. Although glaciation is well documented from the southern paleolatitudes, the low-latitude tropics have long been considered uniformly warm. We hypothesize that alpine glaciation occurred in relatively low-elevation regions of tropical Pangaea. This hypothesis has been widely criticized as “outrageous” and remains poorly accepted; if valid, however, it implies globally cool temperatures at least episodically during the late Paleozoic Ice Age, and raises major questions about how this could have occurred.