One of the main accompllishments of Justinian was-

Question

stopping the Islamic conquest of Wwstern European territories
stopping the Islamic conquest of Wwstern European territories

reconquering some territory that had once belonged to the Roman Empire
reconquering some territory that had once belonged to the Roman Empire

making Christianity the officaial religion of the Roman Empire
making Christianity the officaial religion of the Roman Empire

defeating an invading army of Ottoman Turks and holding the City of Constantinople until the 1900's
defeating an invading army of Ottoman Turks and holding the City of Constantinople until the 1900's

Answer 1

One of the main accomplishments of Justinian was reconquering some territory that had once belonged to the Roman Empire. Additionally, another accomplishment was making Christianity the official religion of the Roman Empire.