Completing this iconic building was the capstone of his professional career.

capstone 由 cap（顶部）和 stone（石头）组成，字面意思是"顶石"，指建筑物顶部的最后一块石头。引申为"顶点、巅峰成就"，比喻事业或项目中最重要的部分或最高成就。