Before the royal consecration at Indraprastha the four younger Pandavas are sent out to bring the four directions under Yudhishthira's authority, and Nakula is given the west. The march takes him through the desert country and the western kingdoms, including the lands of his own mother's people, and it is one of the few sustained passages in which he acts on his own rather than as half of a pair. The epic uses these four campaigns to map the world it thinks it is describing, and gives each brother the quarter that suits him.
The same economy governs the year the brothers spend hidden at the court of Virata, which is the most carefully constructed disguise sequence in the epic. Yudhishthira goes in as a brahmin courtier and dice companion, Bhima as a cook and wrestler, Arjuna as a teacher of dance and music living as a woman, Draupadi as a queen's attendant, Sahadeva as a keeper of cattle, and Nakula as Granthika, master of the king's horses. Each cover is the man's real skill with the rank taken off it, which is why the year works as narrative rather than as a trick: they are recognisable to anyone who knows what to look for, and nobody looks.
Horses are Nakula's subject in the way that omens are Sahadeva's. In a text that measures its heroes by archery, the fourth brother is defined by the animal that makes the chariot move, and by the sword rather than the bow.