What is a characteristic feature of Celtic letters?

The characteristic feature of Celtic letters is their rounded forms combined with sharp points. This design element contributes to the distinctive aesthetic of Celtic calligraphy. The curves in the letters are generally smooth and flowing, while the sharp points, often found at the ends of strokes, create a unique contrast and add to the visual interest of the characters. This blend of rounded shapes and pointed accents is emblematic of the Celtic style, differentiating it from more linear or geometric forms of writing.

In contrast, some options highlight features not typically associated with Celtic letters. For example, the emphasis on straight lines with no curves does not reflect the smooth and rounded nature of Celtic script. Additionally, the notion of thick and thin contrast strokes, while present in various calligraphic styles, doesn't specifically capture the rounded yet pointed essence of Celtic letters. Finally, the idea of only vertical and horizontal strokes limits the expressive quality found in Celtic calligraphy, which thrives on the combination of curves and pointed details. Thus, rounded forms with sharp points accurately encapsulate the defining traits of Celtic letters.