Palenque: The Palace [January 1, 2004]

"Technologically, the Maya must be classified as Stone Age artisans, since all sculpture, architectural construction, and lapidary art were executed without the use of metal. Preferred sculptural media were the softer, more pliable stones, such as the limestone characteristic of the Maya Lowlands.

To some degree stylistic development was formed by the properties of locally available stone. For example, Palenque sculptors preferred wall-mounted slabs to stelae, perhaps because their local limestone, although an excellent medium for relief, was too brittle to use for freestanding stelae."

Schele & Miller, The Blood of Kings, p. 33