From the World Heritage inscription:
The ruins of Quirigua retain an impressive series of stelae and sculpted calendars, partially deciphered, which constitute a remarkable and unique source of the history of the social, political and economic events of the Mayan civilization. The zoomorphic and anthropomorphic sculptures are among the most attractive pre-Columbian works known.
Quirigua is, together with that of Copán (Honduras), one of the major testimonies to the Mayan civilization. At Quirigua, traces of human occupation are attested to from about AD 200, but the zenith of the city may be placed during the period known as Late Classic, about AD 600-900.
Inhabited since the 2nd century AD, Quirigua had become during the reign of Cauac Sky (723-84), the first sovereign of the historic period who has been identified with certainty, the capital of an autonomous and prosperous state. The extraction of jade and obsidian in the upper valley of the Rio Motagua, which was tightly controlled, gave rise to a profitable goods trade with the coastal ports of the Caribbean. This monopoly remained in existence during the 9th century.
Quirigua isn’t the most sexy of Mayan ruins. It is significantly smaller than most sites like Tikal, Copan, or Coba. What buildings are left are not that large and it lacks the awe inspiring pyramids of a Chichen Itza.
What it does have is perhaps the best collection of intact Mayan stelle in the world. Not only are the stelle in relatively good condition, but they are also the largest stelle in the world. In fact, they are the largest pre-Columbia stone sculptures in the Americas.
Quirigua is often considered a companion to Copan in Honduras. If you are visiting Copan, a trip to Quirigua only takes about 1-2 hours, depending on time at the border and traffic. The entire site can be explored in about an hour.
View my complete list of UNESCO World Heritage Sites.