Alwar was a part of the Matsya Kingdom (Matsya is Sanskrit for "fish". Matsya is sacred to Hindus as it is one of the avatar (incarnation) of Hindu deity Vishnu which has been described in detail in Matsya Purana. Matsya kingdoms usually have the fish in their state emblem.), one of the sixteen ancient Mahajanapadas(The Mahajanapadas (Sanskrit:mahajanpad lit. 'great realm', from maha, "great", and janapada "foothold of a people") were sixteen kingdoms or oligarchic republics that existed in ancient India from the sixth to fourth centuries BCE. Two of them were most probably ganatantras (republics) and others had forms of monarchy. Ancient Buddhist texts like the Anguttara Nikaya make frequent reference to sixteen great kingdoms and republics which had evolved and flourished in a belt stretching from Gandhara in the northwest to Anga in the eastern part of the Indian subcontinent and included parts of the trans-Vindhyan region, prior to the rise of Buddhism in India.)
The history of Alwar dates back to 1000 CE. The king of Amer Maharaja Alaghraj(the former seat of Jaipur state) ruled the area in the eleventh century and his territory extended up to the
present-day city of Alwar. He founded the city of Alpur in 1106 Vikrami samvat (1049 CE) under his own name, which eventually became Alwar. From time to time, a different Rajput sub-clan
came to rule Alwar. Examples include the Khanzada Rajputs, the Nikumbh , the Badgujjar , and finally the Naruka (Kachwaha) Rajputs who took the control over this area. Bhadanakas (Bhadana) clan
of Gurjar, The Maratha Empire also ruled this region for a short period. A Rajput, Partap Singh, took the Alwar Fort from the Jat Raja of Bharatpur and laid down the foundation for modern day
The Hindu King Hemchandra Vikramaditya (Hemu), born into a Brahmin family in Machari, Rajgarh, a village in Alwar, was a Hindu emperor of North India during the 16th century. This was a period when the Mughals and Afghans were vying for power in the region. Hemu acceded to the throne of Delhi on 7 October 1556 after defeating Akbar's Mughal forces in the Battle of Delhi in the Tughlakabad area in Delhi, and became the de facto king. He won twenty-two battles in succession and became the last Hindu emperor of North India before the seventeenth century Maratha Empire
Alwar acceded to the dominion of India following the independence of India in 1947. On 18 March 1948, the state merged with three neighbouring princely states (Bharatpur, Dholpur and Karauli) to form the Matsya Union. On 15 May 1949, it was united with neighbouring princely states and the territory of Ajmer to form the present-day Indian state of Rajasthan. Alwar was designated as part of the National Capital Region, resulting in additional development projects including rapid-rail to Delhi and drinking water improvements.The military cantonment of Itarana lies on the outskirts of Alwar.
There are many theories about the derivation of the name Alwar. Cunningham holds that the city derived its name from the Salva tribe and was originally Salwapur, then, Salwar, Halawar and eventually Alwar. According to another school it was known as Aravalpur or the city of Aravali (A Hill system dividing Rajasthan roughly into third and two-thirds). A research conducted during the reign of Maharaja Jai Singh of Alwar revealed that Maharaja Alaghraj, second son of Maharaja Kakil Dev of Amer (old seat of Jaipur State) ruled the area in the eleventh century and his territory extended up-to the present city of Alwar. He founded the city of Alpur in 1106 Vikrami Samvat (1049 A.D.) after his own name (Maharaja Alaghraj) which eventually became Alwar from Alpur. It was formerly spelt as 'Ulwar' but in the reign of Jai Singh the spelling was changed to 'Alwar'.