The ancient castle's high walls were supported by strong buttresses.

buttresses 是名词 buttress 的复数形式。buttress 来自古法语，指建筑物外部的支撑结构，用于加固墙壁或拱门，防止倒塌。在建筑学中特指"扶壁"或"拱壁"，通常呈斜角或半圆形突出于墙面。