Complex sentence: Gower's final Test century was scored in January 1991, when he reached 123 against Australia: half of Gower's eighteen Test centuries came during Ashes contests, the fourth most by any batsman.
Split into simpler sentences: Gower's final Test century was scored in January 1991, when he reached 123 against Australia. In total, nine of Gower's eighteen Test centuries came during Ashes contests, the fourth most by any batsman.