Graffiti has been found gouged into Saiin-Ogaki, a wall at Horyuji Temple in Ikaruga, Nara Prefecture, the prefectural board of education said Wednesday.
The two scribbled messages translate as "I'll kill you" and "you must have nothing to do" in the Kansai dialect.
Horyuji Temple contains more than 2,300 cultural and historical items, including 19 structures, designated as national treasures or important cultural properties. It was registered by UNESCO as a World Heritage site in 1993.
Saiin-ogaki is a large wall surrounding the "saiin," or western precinct, of the temple grounds. This section contains Kondo, the main hall, and Goju-no-to, the five-storied pagoda. The wall lines the eastern, southern and western sides of the area.
The graffiti was found gouged 6 mm deep into the wall's western section, which is 3.5 meters tall and 70 meters long. They were placed about a meter above the ground.
The board of education speculates they were carved with a screwdriver or other sharp tool.
As the wall was constructed using "rammed earth," an ancient building technique where successive layers of soil are compressed to ensure durability and thermal quality, it is impossible to cover the graffiti with paint.
"It will be very difficult to remove the scribbles from the wall, as to do so we would need to scrape the surrounding surface," the board said in a statement.
It said officials are considering other measures to make the graffiti less noticeable.