sentences:  The main feature of the site is a group of three Maya stelae and an altar, arranged in a way that mimics an E-Group Maya astronomical complex.Tres Islas is one of only a few Maya cities that erected dated monuments in the Early Classic period (c. AD 250 - 600).Tres Islas is situated on the west bank of the Pasión River in the municipality of Sayaxché in Guatemala's northern department of Petén.