The desecration at Mehrauli was probably the first perpetrated by Muhammad Ghauri. It is situated next to the famous Qutb Minar. The masjid was named after its builder, Qutbuddin Aibak, as Quwwatul Islam, which, translated into English, means the Might of Islam. The name itself is arrogant; for a place of worship it is even more so.
Let us quote the version given in the Oxford History of Islam: The immense congregational mosque in Delhi known as Quwwat al-Islam (Might of Islam) was one of the first built in India. Begun in 1191, the mosque stands on the site of a pre-Islamic temple whose ruins were incorporated in the structure. The tall iron pillar in the courtyard, originally dedicated to the Indian god Vishnu around 400, was re-erected as a trophy to symbolize Islam's triumph over Hinduism.
However, when one reads what Sir Syed Ahmed Khan of Aligarh fame proudly wrote about the destruction of 27 temples, one's impression of Islam gets shaken. What he wrote is best read in his original words, (from his Urdu book, Asar-us-Sanadid, translated by Prof. Khaleeq Anjum, Delhi in 1990, Volume I):
Quwwatal-Islam Masjid'd Din Sam alias Shihabu'd-Din Ghauri, conquered Delhi in AH 587 corresponding to AD 1191 corresponding to 1248 Bikarmi, this idol-house (of Rai Pithora) was converted into a mosque. The idol was taken out of the temple. Some of the images sculptured on walls or doors or pillars were effaced completely, some were defaced. But the structure of the idol-house kept standing as before.
Material from twenty-seven temples, which were worth five crore and forty lakh of Dilwals, were used in the mosque, and an inscription giving the date of conquest and his own name was installed on the eastern gate.
When Malwah and Ujjain were conquered by Sultan Shamsu'd-Din in AH 631 corresponding to AD 1233, then the idol-house of Mahakal was demolished and its idols as well as the statues of Raja Bikramajit were brought to Delhi, they were strewn in front of the door of the mosque.