There are several synonyms for the phrase "a monument to something." One such synonym is "a symbol of," which implies that the object represents something significant and serves as a reminder of its importance. Another synonym is "a tribute to," which suggests that the object commemorates a specific event or person and acknowledges their contributions or achievements. Additionally, the phrase "a testament to" can be used to describe something that serves as evidence or proof of a particular idea or concept. Ultimately, all of these synonyms convey the idea of something being worthy of recognition and commemoration in a significant way.