Answer: Just prior to the start of his reign, Palenque had been sacked by a neighboring city.
When K'inich Janaab' Pakal ascended to the throne in 615, he was 12 years old. In 605, Palenque was attacked by Kaan (or Calakmul/Kalakmul), a neighbouring city, and a new ruler was instated. Kaan attacked the city again and sacked it in 610 and 611.
However, Palanque flourished under Pacal's rule and produced some of the finest Mayan art and architecture.