An armilla is a model of the Earth that allows it to revolve on an axis and shows features like the equator and the tropic of Cancer. Armillas are among the very oldest instruments used by astronomers.
Another name for an armilla is an armillary sphere or an astrolabe. In ancient Greece, armillas were one of the primary astronomical tools used by scientists for teaching and observation. Another kind of armilla, also present in the ancient world, was a military armband awarded to ancient Roman soldiers for bravery or gallantry. In Latin, the word literally means "bracelet," from armus, "shoulder or upper arm."