Whittemore and his team of experts worked in Hagia Sophia until the outbreak of World War II and then resumed work again as soon as hostilities ceased. Their working season lasted for some seven months, from spring until autumn, but ceased in winter when the temperatures inside the building fell too low. The team’s main task was to undo the work of the Fossati brothers by revealing the figural mosaics they had concealed between 1847 and 1849 with paint and plaster.