Final answer:
St. Augustine met St. Ambrose in 386 A.D. in Milan, which was one year before Augustine's celebrated conversion to Christianity in 387 A.D.
Step-by-step explanation:
St. Augustine met St. Ambrose in 386 A.D., one year before his conversion, which took place in 387 A.D. Augustine moved from his birthplace in Roman Numidia to Carthage at the age of seventeen and later to Milan, where he came under the influence of St. Ambrose. This meeting was significant as Ambrose's teachings greatly influenced Augustine's conversion to Christianity.
After his conversion, Augustine returned to North Africa, took up the bishopric of Hippo, and engaged in theological debates, notably against the Donatist rift. He remained a key figure in the church, defending orthodox Christianity against various heresies, and his work, The City of God, became seminal for Christian thought concerning the relationship between the earthly realm and the heavenly.