What instrument is described as a small U-shaped harp with strings fixed to a crossbar?

The description of a small U-shaped harp with strings fixed to a crossbar accurately fits the definition of a lyre. The lyre is an ancient stringed instrument characterized by its distinctive shape, which resembles a U, and its string arrangement that is often attached to a crossbar. This instrument has a rich history in various musical traditions and is notably associated with ancient Greece, where it was used in both solo performances and as an accompaniment to poetry recitation.

In contrast, the guitar is a different type of string instrument with a flat body and typically a larger size compared to the lyre. The harp has a larger frame, characterized by its triangular shape, and is usually much bigger than a lyre. The violin, while also a stringed instrument, is smaller and has a different construction and shape altogether.

The unique features and historical context of the lyre solidify it as the instrument that matches the given description effectively.