The Brahmana and the Kshatriya are connected with each other by nature, and each protects the other. The Kshatriya is the root of the Brahmana's advancement and the Brahmana is the root of the Kshatriya's advancement.
एतौ हि नित्यं संयुक्तावितरेतरधारणे। क्षत्रं वै ब्रह्मणो योनिोनिः क्षत्रस्य वै द्विजाः॥