When Mongol massacred People of Lahore and levelled the city.

As per Dr. Balaji Sadasivan (A Singaporean politician and neurosurgeon):

“The ancient city of Lahore has no buildings or large monuments that pre-date 1241. In that year the mongol massacred its inhabitants and levelled the city. The cities of north India faced a similar fate but they were saved by the Turkish slave general, Balban, who halted the mongol advance into India and pushed them out of Punjab.”

The Dancing Girl: A History of Early India, Page 161