 As chief architect to the "Comité de Conservation des Monuments de l'Art Arabe", he directed the conservation of monuments of Arab-Islamic and Coptic architecture all over Egypt, first of all in Cairo from 1890 until the end of 1914.Upon the outbreak of World War I, at the end of 1914, Herz, a Hungarian citizen, was forced into retirement and expelled from the country as an enemy alien by the British authorities; though officially an autonomous province of the Ottoman Empire with special rights, Egypt had been under British military occupation from 1882 on.Leaving all his possessions behind, he went to Milan with his family, where the relatives of his Italian wife lived.