Aquila
In 106, Gaius Marius made the aquila(eagle) the main military standard as part of his reforms of the roman military. The eagle was typically made of gold or silver and gold plated and was carrying a thunderbolt in its talons, which represented the army's readiness to fight. It had raised wings that sometimes had a laurel wreath around them. Right above the eagle, there was a gold banner with the letters SPQR(the senate and the people of Rome) which honored the Roman Senate and people. The legatus(general) would assign one of the soldiers to be the aquilifier(eagle carrier) who would carry the aquilla into battle. However, unlike most standard-bearers, he did not wear any animal skin. He normally wore a helmet and he carried a parma(small circular sheild) that could be strapped to his arm if his hands were full. In 53, Crassus and his men lost 7 aquilla standards in the Battle 0f Carrhae.
Fun Fact: When the Roman was split into the eastern and western empires, the eastern emperor Issac used the single-headed eagle was changed to a double-headed eagle to symbolize the Empire's control over both east and west.