The Iberians:
There was a dark-haired race know as the Iberians, who lived in "Britain" 1,000's of years before the Celts arrived. They were hunters and shepherds, who were also adept at weaving and crafts.
Stonehenge:
On the Salisbury Plain in southern England near Southampton is an ancient site made of huge stones or megaliths (a single stone is a monolith). They were raised circa 3000-1500 BC, in several stages. Its design was based on geometry and astronomy.
The main purpose for Stonehenge was as an astronomical calendar, the stones aligned with the summer and winter solstices and other solar and lunar events. It also might have been used as a location for pre-Christian religious ceremonies.
Who built Stonehenge is a matter of opinion, the guesses range from the Iberians to the Druid priests.
The design (described as if all the stones are still standing):
There are two complete circle of stones. The outer circle consists of large sarsen stones named the "Sarsen Circle". “Lintel" stones laid horizontally across their tops, meeting each other at either ends to form a circle, top them.
There is circle of smaller stones inside the Sarsen Circle. This is called the "Bluestone Circle". They do not have lintel stones.
Then there are ten Sarsen Stones with lintels, taller than the other Sarsen Stones. Also know as trilithons, these immense stones numbering ten are set in five pairs, two stones to each pair. They form a horseshoe shape; the two in the "heel" of the "horseshoe" are larger than the other eight.
Then comes more bluestones, also set in a horseshoe shape and there is an altar stone set in the inner-bluestones in the "heel".
The midsummer sunrise shines on the center pair of inner-Sarcen Stones entering through the "horseshoe", the setting sun hits the center pair of inner-Sarcens from the other direction.
Encircling all these immense stones are two more circles, called "y holes" and "z holes".
"STONEhenge? I've got an uncle who comes from there!"
Height and weight of the Stonehenge stones (all estimates):
The Sarcen Circle stones are 18' tall and 25 tons.
The lintels over the Sarcen Circle stones are 10' long and 6 tons.
The bluestones are 14' tall and can weigh as much as 4 tons.
The eight larger inner-Sarcens are 22' tall and 50 tons.
The two largest inner-Sarcens are 30' tall and 60 tons.
The lintels over the inner-Sarcens are 14' long and 12 tons.
The bluestones that make the "horseshoe" are 14' tall and up to 4 tons.
The altar stone in the inner-bluestone "horseshoe" is 10' long and 6 tons.
Transporting the stones:
The Sarsen Stones were taken from a site 24 miles away in Marlborough Downs. The bluestones (more than 80 of them) were transported by raft from a site in the Prescelly Mountains in southwestern Wales, 140 miles away.
Possible builders:
1700 BC, "Beaker" People from Holland and Rhineland migrated to southern Britain. They merged with the inhabitants and formed the Wessex People. They, along with the previous inhabitants, had a hand in the construction.
Celtic tribes to Britain:
From the 7th to 3rd c. BC Celts (a.k.a. Gaels) moved across western Europe to Britain. Some tribal names were the Belgae, Cantii, Cymri and Brythons (from where the name Britain comes from). These Celts raised several types of grain, had livestock and kept bees, were skilled at crafts and carpentry and worked with iron. They also had horses and chariots. The well-known King Arthur (late 5th c. to early 6th c. AD) was a Briton. Their priests were the Druids and "Old King Cole" was their god of war.
The inhabitants of northern Britain were Celts who called themselves the Cruithni. The Romans called them Picts and their territory Caledonia. The Picts ruled northern Britain until the 7th century. The Scots, known as the Dalriada, migrated to northern Britain during the 6th and 7th centuries. They fought with and absorbed the Picts, whose particular name and culture disappeared from history by the 9th century. (The Scots were also known as the Scotti and while in Ireland called themselves Féni.)