The area of Santiago de Compostela was a Roman cemetery by the 4th century and was occupied by the Suebi in the early 5th century, when they settled in Galicia and Portugal during the initial collapse of the Roman Empire. In the 8th Century, Muslim Moors raided the city.
In the 9th century, a hermit named Pelagius contacted the local Bishop Theodemar of Iria after seeing strange lights in the sky above a field. When the Bishop investigated the field, he discovered the partially buried bones of St. James. The star-field or Campus Stellæ was built up into a shrine.
The Shrine was drawing pilgrims by the 11th century in large numbers. These pilgrims provided meaningful financial and moral aid to the soldiers engaged in the Reconquista to drive the Muslims out of Spain.
While the origin legends are, well, legend-like, the more mundane assertion that the shrine is just a medieval fundraiser don't account for the ongoing popularity of the Camino and the multitude of miraculous events along the path over the course of eight centuries.
Construction of the present cathedral began in 1075 using the same basic plan as the Cathedral in Toulouse, France. The last stone was laid in 1122. Final construction and the consecration didn't take place until 1211 undrr the watchful eye of King Alfonso IX of León.
The Cathedral is a wonder to behold. Each of it's sides has an astounding façade and each façade forms one side of an amazing plaza or city square.
More on the design and detail here.
The name "Botafumeiro" means "smoke expeller" in Galician. The Botafumeiro in Santiago is truly one of a kind. It is a gigantic censor. And gigantic is the word. The Santiago de Compostela Botafumeiro is one of the largest censers in the world, weighing 80 kg (~176 lbs.) and measuring 1.60 m (5'3") in height.
The Botafumeiro is suspended from a pulley mechanism in the dome on the roof of the church. The current pulley mechanism was installed in 1604. The ropes typically last about 20 years before they have to be replaced.
The present Botafumeiro is made of an alloy of brass and bronze and is plated by a very thin 20 micrometre layer of silver. The current Botafumeiro was created by the gold and silversmith José Losada in 1851. It has a golden sheen.
There is another large thurible used in some masses in the cathedral, called "La Alcachofa" (literally, "The Artichoke") or "La Repollo" (literally, "The Cabbage").La Alcachofa is a silver-colored metal censer. It was created in 1971 by the sacred art artisans working under the craftsman Luis Molina Acedo.
Shovels are used to fill the Botafumeiro, or the Alcachofa, with about 40 kg (~88 lbs.) of charcoal and incense. At the top of the swing, the Botafumeiro reaches heights of 21 meters. It swings in a 65-meter arc between the Azabachería and Praterias doorways at the ends of the transept. The maximum angle achieved is about 82°. The maximum can be reached after about 17 cycles, and requires about 80 seconds of swinging.
The Botafumeiro is carried and swung by eight men in red robes, called tiraboleiros. The term "tiraboleiro" is a Galician derivation from the Latin word "turifer", which means "incense carrier", and from which is derived the English equivalent, "thurifer". This comes from the Latin words "thus", meaning incense, and "fero", meaning "carry". There is a comparable term in Spanish, a "turiferario".