The National Epic greatly increases the rate at which its city produces Great People, particularly Great Artists.
This wonder should be built on your best food city so you may work the greatest number of specialists and produce the greatest number of Great People. Civic switch to Caste System and Pacifism for maximum effect.
An "epic" is a heroic poem celebrating the life and achievements of a heroic individual or group. Classic examples of epics include Homer's "Iliad" and "Odyssey."
A "national epic" celebrates the exploits of an entire country. One of the earliest examples is the "Shahnama" (The Book of Kings), a Persian literary classic written around 1000 AD. The Shahnama chronicles the history of Persia from mythological pre-history through the reign of Khosrau II (590-628). The work contains over 60,000 couplets and is still read and enjoyed by modern readers.
It is possible that the age of the literary epic is dead, and that in the future all such stories will be done as "made for TV movies." This would be a great misfortune to the world of letters - and to the rest of the world, as well.