Arthashastra
प्रहरण विद्या विनीतं तु क्षत्रिय बलं श्रेयः, बहुल सारं वा वैश्य शूद्र बलम् इति ॥
Hence, the army of Kshatriyas trained in the art of wielding weapons is better; or the army of Vaisyas or Súdras having great numerical strength (is better).
english translation
praharaNa vidyA vinItaM tu kSatriya balaM zreyaH, bahula sAraM vA vaizya zUdra balam iti ॥
hk transliteration by Sanscript