Complex sentence: From 1850 onwards piecemeal repairs were carried out frequently, but under the supervision of the Badshahi Mosque Authority, thorough repairs were carried out from 1939 to 1960 at a cost of about 4.8 million rupees, which brought the mosque to its original shape and condition.
Split into simpler sentences: From 1850 onwards, piecemeal repairs were carried out under the supervision of the Badshahi Mosque Authority. Extensive repairs were carried out from 1939 to 1960 at a cost of about 4.8 million rupees, which brought the mosque to its original shape and condition.