Around 2000 BC, when the priests in Babylon were conducting, and recording, their observations of the celestial bodies, the building of the first phase of Stonehenge was begun.

Over the next six hundred years a series of successive structures were erected and Stonehenge as we know it finally arose around 1400 BC.

The approach, from the northeast, follows the ditch bordered 'Avenue' past the 'Heel' stone with its surrounding ditch and through the thirty five feet wide gap in the bank. 

There would seem to have been, at some time two, standing stones in the entrance gap.

The 'Four Stations' or 'Station Stones' stand inside the bank more or less on the 'Aubrey Hole' circle.  They form a rectangle whose sides and diagonals possess what Gerald Hawkins called 'astronomic significance.'  Only at, or very close to, the latitude of Stonehenge ( 51' 10" ) do these alignments form a rectangle and this may be why Stonehenge was sited where it is  ' The implications of this are that the builders of Stonehenge had a knowledge of the global nature of the Earth' - Devereux

Between the 'Aubrey' holes and the central stones are two rings of holes, picturesquely called the 'x' and 'y' holes. As with the 'Aubrey ' holes there is little archaeological evidence as to the function of these holes. Curiously practically almost every pit excavated held a bluestone chip, specifically rhyolite, near the bottom. 

A similar rhyolite chip was found at the bottom of the ditch surrounding the 'Heel' stone.

The central part of the monument comprises several concentric stone arrangements; the outermost of which are the thirty stones of the 'Sarsen circle.' The sarsen (hard sandstone) stones were probably transported from the Marlborough Downs; about twenty miles to the north-east of Salisbury Plain. The average error in the spacing of these huge stones standing on a circle, ninety-eight feet in diameter is somewhere in the region of four inches. These 'smaller' sarsen uprights weigh around twenty five tons compared to the forty-five to fifty tons of the larger central stones. 

The entrance to the sarsen circle is to the northeast. 

Inside the sarsen circle is a circle of 'bluestones'

enclosing the trilithons, five linteled triads of large sarsen stones laid out in the shape of a horseshoe, open to the northeast.

A smaller bluestone horseshoe within the trilithons is similarly aligned. 

Almost at the geometrical centre of Stonehenge lies the 'Altar' stone, a pale greenish/brown micaceous sandstone. 

This stone was brought to the monument from the area around Milford Haven in Southwest Wales.