Mughal emperor Humayun built the city of Dinpanah (meaning 'refuge of the faithful') at the site of present-day Purana Qila in Delhi in the 1530s after his return from exile. This was his attempt to establish a new capital. Other options - Ajmer (already existed), Chausa (site of Humayun's defeat), Daulatabad (built by Muhammad bin Tughlaq) - are incorrect.