In 1889 he succeeded Edmond Duthoit as chief architect of the historical monuments department in Algeria, a position which he held for 30 years. Like his predecessor, Ballu was an advocate of regionalism and protection of the local heritage. He designed the Algerian pavilions and a reproduction of an Algerian town for the Paris Expositions 1889 and 1900. He participated in and from 1889 directed the excavations of the ancient Roman cities of Djémila and Timgad.