Samarra first drew the attention of archeologists around the turn of the 20th century, and excavation work was conducted by Henri Viollet, Friedrich Sarre, and Ernst Herzfeld in the period leading up to World War I. Aerial photographs were taken between 1924 and 1961, which preserved portions of the site that have since been overrun by new development. The Directorate-General of Antiquities of Iraq restarted excavations between 1936 and 1940, and continued in the 1960s and 1970s. Excavation and restoration work took place between 1980 and 1990. Around the same time, Alastair Northedge surveyed the surviving portions of the city, and has since published several works on the subject. Despite these projects, an estimated 80% of the site was still unexcavated around the beginning of the 21st century.