Final answer:
The primary material of Yaxchilan by the Maya in 725 CE is limestone. This material was commonly used by the Maya due to its availability and carvable nature that hardened over time, ensuring the longevity of their structures.
Step-by-step explanation:
The primary material used in the construction of Yaxchilan, an architectural complex by the Maya on the Yucatán Peninsula in 725 CE, is limestone. This choice is supported by historical records and archaeological evidence which indicate that the Maya civilization, particularly during the Mayan Classic Period (250 CE - 1539 CE), frequently used limestone for their construction projects. Limestone was abundant in the region, and its relative softness when quarried made it easier to carve; however, it hardened over time after being exposed to the elements, providing durability for the structures. The site of Yaxchilan is known for its beautiful limestone constructions, which include impressive temples, palaces, and stelae inscribed with hieroglyphic script.