Raja Ajaipal of the Chauhan Rajputs established Ajmer in the tenth century. Located at the foot of the Taragarh Hill, it is about 228 miles (367 kilometers) west of Agra. The name, Ajmer, is a composition of 'ajya' (invincible) and 'mer' (hill) and literally stands for 'invincible hill'. The Taragarh Fort is located at the summit of this hill. Due to its strategic location, it was the administrative center of the Chauhans. 

In 1024, it was sacked by Mahmud of Ghazni, falling later, in 1193 to Muhammad Ghuri after the second battle of Tarain. Ajmer was integrated intothe Delhi Sultanate and was held by the rulers of Malwa between 1470-1531.

Ajmer maintained its strategic importance even during the Mughal era; in 1556, Akbar established his royal residence there. Akbar's palace is located in the middle of the city and is now the Ajmer Museum. A row of pavilions built by Shah Jahan can be found at the edge of the artificial lake, Ana Sagar, built by Raja Anaji between 1135-1150. Under Jahangir, beautifully landscaped gardens were laid out around the lake. Other additions to the city by the Mughals include the Akbar's Masjid (1570) and Shah Jahan's Masjid (mid-seventeenth century). The fall of the Mughals brought the city under the rule of the Jodhpur and later the Marathas. In 1818, became part of the British administration. The British founded Mayo College there in 1875 to provide English education for young Indian princes. 

The most important religious building here is the Dargah of Khawaja Muin-ud-Din Chishti (1143-1235), the tomb of a Sufi saint known as the 'Sun of the Realm of India'. It is an important pilgrimage site for both Muslims and Hindus. It was began by Iltutmish and carried to completion by Humayun. The Arhai Din Ka Jhompra Masjid is another important building due to its status as an early example of Indo-Islamic architecture. 

Sources:

Davies, Philip. The Penguin Guide to the Monuments of India - Volume 2: Islamic, Rajput, European. London: The Penguin Group,1989. 

Lonely Planet Travel Guide - India. London: Lonely Planet Publications, 1999.

DK Eyewitness Travel Guides - India. London: Dorling Kindersley Limited, 2002.