"At that time" is a common expression used in writing and speech to refer to a specific moment or period in the past. However, using the same phrase over and over can become monotonous and unengaging for readers or listeners. Therefore, it is important to broaden your vocabulary and have alternative words or phrases to express the same idea. Some synonyms for "at that time" include "then, back then, in those days, during that period, during that moment, previously, formerly, and in the past." Employing these synonyms can help your writing or speech become more interesting and captivating.