The 63 step hieroglyphic staircase is the longest known Mayan hieroglyphic inscription -- it's certainly the longest propaganda piece! The 15th ruler Smoke Shell (as he is commonly called) had the staircase created in 743 AD to record the history of his ancestors.  In effect justiying his position; to connect the dots (just in case the citizens of Copan might be questioning) between him and the revered Yax Kuk Mo, who founded Copan circa 160 AD. 

Its inscriptions are worn-down so in order to prevent further erosion, it is now protected by an enormous tarpaulin.