The Inca told their beginning in two ways, and the chroniclers recorded both without reconciling them.
In the first, the sun sends Manco Capac and his sister and consort Mama Ocllo out of Lake Titicaca to bring order to people living without agriculture or law, giving them a rod of gold and telling them to settle where it sinks into the ground. They travel north, the rod sinks in the valley of Cusco, and the city is founded there. The version is cosmological, it makes the dynasty the direct gift of the solar deity, and it is the one Garcilaso de la Vega set down.
In the second, four brothers and four sisters emerge from a cave at Pacaritambo, south of Cusco. The journey is long and the brothers are eliminated on the way: one is sealed in a cave by a trick, another is turned to stone at the shrine of Huanacauri, another becomes a stone in the city itself. Only Manco Capac reaches Cusco with the women and the founding is achieved by attrition among kin. This is the version in Betanzos and in Sarmiento.
The two are not careless variants. The first grounds the dynasty in the sun and in the sacred lake at the centre of an older ceremonial world; the second grounds it in a specific cave that could be visited, in a lineage with named siblings, and in petrified ancestors who remained as shrines. Both were current in the sixteenth century, and both encode a claim about where authority in Cusco came from.