Complex A is a mound and plaza group located just to the north of the Great Pyramid (Complex C). The centerline of Complex A originally oriented to Polaris (true north) which indicates the Olmec had some knowledge of astronomy. Surrounded by a series of basalt columns, which likely restricted access to the elite, it was erected in a period of four construction phases that span over four centuries (1000 – 600 BCE). Beneath the mounds and plazas were found a vast array of offerings and other buried objects, more than 50 separate caches by one count, including buried jade, polished mirrors made of iron-ores, and five large "Massive Offerings" of serpentine blocks. It is estimated that Massive Offering 3 contains 50 tons of carefully finished serpentine blocks, covered by 4,000 tons of clay fill.