Rajapura or Rajapuram was the capital of the ancient Kamboja Kingdom mentioned in the Mahabharata. Karna led a war expedition against the Kamboja and some other tribes of the Uttarapatha a little time before the Kurukshetra war i.e. Karana Rajapuram gatva Kamboja Nirjitastvaya. The Chinese pilgrim Xuanzang who travelled to India in the 7th century refers to Hoshepulo which has been identified as Rajapura of Sanskrit tradition by Watters and others.
Map of Rajapura, Karnataka 583115
References
Rajapura (Kamboja) Wikipedia(Text) CC BY-SA