Complex sentence: The stone is believed to have been an important astronomic clock or calendar by the Incas and used to tell the time, aligned with four important mountains, and aligned directly at the sun during the winter solstice.
Split into simpler sentences: The stone is believed to have been an important astronomic clock or calendar of the Incas. Used to tell the time, it was aligned with four important mountains the sun's position during the winter solstice.