How was Stonehenge built?

It is likely that we will never know for sure how the
people who created Stonehenge managed to do so without any modern technology.  Scholars
guess about this sort of thing all the time, but there is no way to definitively prove
how it was done.

The biggest mystery surrounds the way in
which the stones were transported to the building site.  Scholars have speculated about
various ways of making this possible.  They have speculated that logs were placed on the
ground in the path of the stones and used as rollers to allow the stones to move more
easily.  They have speculated that the people set up wooden tracks and pulled the stones
on sleds over the tracks.  These tracks might have been lubricated with
grease.

Once the stones were at the site, one assumption is
that ramps of earth were built so that the lintels could be dragged up to be put in
place.

All of these are informed guesses.  There is no way
to actually know for sure.