Srimad Bhagavatam Canto 04, Chapter 17, Text 09

SB 4.17.9

maitreya uvaca
yadabhisiktah prthur anga viprair
amantrito janatayas ca palah
praja niranne ksiti-prstha etya
ksut-ksama-dehah patim abhyavocan
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The great sage Maitreya continued: My dear Vidura, at the time King Prthu was enthroned by the great sages and brahmanas and declared to be the protector of the citizens, there was a scarcity of food grains. The citizens actually became skinny due to starvation. Therefore they came before the King and informed him of their real situation.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Information is given herein concerning the selection of the king by the brahmanas. According to the varnasrama system, the brahmanas are considered to be the head of the society and therefore to be situated in the topmost social position. The varnasrama-dharma, the institution of four varnas and four asramas, is very scientifically designed. As stated in Bhagavad-gita, varnasrama-dharma is not a man-made institution, but is God-made. In this narration it is clearly indicated that the brahmanas used to control the royal power. When an evil king like Vena ruled, the brahmanas would kill him through their brahminical powers and would select a proper ruler by testing his qualifications. In other words, the brahmanas, the intelligent men or great sages, would control the monarchical powers. Here we have an indication of how the brahmanas elected King Prthu to the throne as the protector of the citizens. The citizens, being skinny due to hunger, approached the King and informed him that necessary action should be taken. The structure of the varnasrama-dharma was so nice that the brahmanas would guide the head of state. The head of state would then give protection to the citizens. The ksatriyas would take charge of protecting the people in general, and under the protection of the ksatriyas, the vaisyas would protect the cows, produce food grains and distribute them. Sudras, the working class, would help the higher three classes by manual labor. This is the perfect social system.
Srimad Bhagavatam Canto 04, Chapter 17, Text 08
Srimad Bhagavatam Canto 04, Chapter 17, Text 10-11