“La Folia” (also spelled “La Follia”) is both a musical theme and a chord progression which seems to date from Renaissance Spain, and has probably had more variations written on it than any theme in history. Here, for example, is the chord progression:
and here it is as a theme:
Both these examples are taken from La Follia, A Musical Cathedral, which is a magnificent resource for information about this fascinating piece of music.
Almost all composers of the late Renaissance and baroque wrote some variations on La Folia, (Bach’s exist as a set for two violins accompanying the aria “Unser trefflicher lieber Kammerherrin” from the “Peasant Cantata”, BWV212.)
A particularly splendid and spirited set is that of Vivaldi, for two violins and continuo.
Here it is in its original version:
Unfortunately this video cuts in part way through the introductory theme, but the rest is brilliant.
And here’s a version arranged for string orchestra, where the performers given it “their all”: