What does the term aquila refer to in a military context?

The term "aquila" in a military context specifically refers to the eagle standard of a Roman legion. This standard was a symbol of the legion's honor and unity, often represented by a depiction of an eagle, which was believed to carry the soul of the legion and protect the soldiers. The aquila was a crucial part of the Roman military structure, serving not only as a rallying point for troops in battle but also embodying the spirit and pride of the legion. Losing the aquila in battle was considered a significant disgrace, as it symbolized the loss of the legion's identity and power.

In contrast, other options such as the shield bearer, war horse, and infantry unit do have their respective military meanings but do not specifically define the term aquila in the same way as the eagle standard does. The shield bearer (or "scutarius") was a soldier tasked with carrying a shield, the war horse was vital for cavalry, and infantry units referred to the standard foot soldiers of the military. Each of these elements contributes to the overall military structure but does not encapsulate the unique significance of the aquila.