Inca flag
 
The Incan flagThere are 16th and 17th century chronicles and references that support the idea of a banner, or flag, attributable to the Inca. Francisco López de Jerez wrote in 1534:

"all of them came distributed into squads, with their flags and captains commanding them, as well-ordered as Turks"
("todos venían repartidos en sus escuadras con sus banderas y capitanes que los mandan, con tanto concierto como turcos").

The chronicler, Bernabé Cobo, wrote:

"The royal standard or banner was a small square flag, ten or twelve spans around, made of cotton or wool linen, placed on the end of a long staff, stretched and stiff such that it did not wave in the air, and on it each king painted his arms and emblems, for each one chose different ones, though the sign of the Incas was the rainbow."
(...el guión o estandarte real era una banderilla cuadrada y pequeña, de diez o doce palmos de ruedo, hecha de lienzo de algodón o de lana, iba puesta en el remate de una asta larga, tendida y tiesa, sin que ondease al aire, y en ella pintaba cada rey sus armas y divisas, porque cada uno las escogía diferentes, aunque las generales de los Incas eran el arco celeste.)
-Bernabé Cobo, Historia del Nuevo Mundo (1653)

Guaman Poma's 1615 book, El primer nueva corónica y buen gobierno, shows numerous line drawings of Inca flags.

In modern times the rainbow flag has been associated with the Tawantinsuyu and is displayed as a symbol of Inca heritage in Peru and Bolivia. The city of Cusco flies the Rainbow Flag. Even the Peruvian president Alejandro Toledo (2001-2006) flew the Rainbow Flag in Lima's presidential palace.

According to the Peruvian newspaper El Comercio, the flag only dates to the first decades of the 20th century. But in his 1847 book A History of the Conquest of Peru, "[ William H. Prescott ] ... says that in the Inca army each company had its particular banner, and that the imperial standard, high above all, displayed the glittering device of the rainbow, the armorial ensign of the Incas." A 1917 world flags book says the Incan "heir-apparent ... was entitled to display the royal standard of the rainbow in his military campaigns."