What do the letters I T mean?

Another method of dating, rarely used, was to indicate the year anno urbis conditae, or "in the year of the founded city" (abbreviated AUC), where "the City" meant Rome. (It is often incorrectly given that AUC stands for ab urbe condita, which is the title of T. Livy's history of Rome.) Several epochs were in use by Roman historians. Modern historians usually adopt the epoch of Varro, which we place in 753 BC.