Answer: St. Ambrose baptized St. Augustine in Milan during the Easter Virgil services of 387.

References
• Make Aquilina and Grace Aquilina, Chapter 25: A Milan Baptistery, A History of the Church in 100 Objects, Ave Maria Press, copyright 2017
• Thomas I Crimando, New Issue - Commemorating The Sixteenth Centenary Of The Conversion And Baptism Of St. Augustine Vatican Notes Volume 35, Issue 6 May 1987, Pages 1 & 3
•  Sixteenth Centenary Of The Conversion And Baptism Of St. Augustine UFN Bulletin 87-03 1987



  

  6th Centenary Of The Conversion Of St Augustine
Scott # 779-782 (1987)