Is the Good, The Bad and The Ugly set before a Fistful of Dollars?

There are subtle clues inside the films to establish their individual timeframes, but no concrete evidence that they are connected in any way beyond the actor Clint Eastwood, and any connecting mannerisms he places in the character. Sergio Leone himself said that it was merely a packaging ploy by the American distribution company to link the films. The best we can do is establish their times by visual clues inside the films themselves.

The Good, The Bad, and The Ugly has grave markers in the military cemetary shown dated 1862 and 1864, while the war is still active, so the events occur in 1864 - 1865.

Fistful of Dollars and For a Few Dollars More has Clint Eastwood's revolver as the "Single Action Army revolver" introduced 1872. Fistful of Dollars has a gravestone dated 1873, and For a Few Dollars More shows a newspaper archive dated 1873. So these films' timeframe is 1873 or later.

So the films show GBU to be at least 7-8 years before the established timeframe of the other two. Plenty of time to lose, spend, or bury those bags of gold, but, since GBU was filmed later, and not intended by Leone to be connected, that's mere conjecture.

Much of this data is attributed to a variety of websites devoted to details of the films and the director, Sergio Leone.

Well, wbogacz already gave a very good answer to the question about the chronology and its clarity. But as to if it was intended or how far it is consistent with the overall story, I think it is rather us audience who just want to draw a connection between different characters where there is none. This motivation lead at least to the coining of the term "Man With no Name"-trilogy, although this man is a completely different character in the particular movies. You wouldn't believe Sentenza to be the same person as Colonel Mortimer just because they were portraied by the same actor, would you? So there isn't anything that makes me believe Clint Eastwood's character to be the same person in The Good, The Bad and The Ugly as in A Fistful of Dollars.

This is to some degree supported by the corresponding Wikipedia article which states:

Although it was not Leone's intention, the three movies came to be considered a trilogy following the exploits of the same so-called "Man with No Name" (portrayed by Clint Eastwood, wearing the same clothes and acting with the same mannerisms). The "Man with No Name" concept was invented by the American distributor United Artists, looking for a strong angle to sell the movies as a trilogy. Eastwood's character does indeed have a name - albeit a nickname - and a different one in each film: "Joe," "Manco," and "Blondie," respectively.

So given that the connection of the third movie to the others was developed after the fact, there is likely no intentional connection between the characters and story of those movies, even if the chronology is pretty definite. Instead of by their backstory and identity, the characters played by Clint Eastwood in those films are rather connected by their traits, mannerisms and style, which might suggested a deeper connection where there is none. And in fact this is IMHO by-design. We are just not supposed to know anything about this man's motives and his story before or after the individual movies, as that's what actually makes him the a "Man with No Name".

Actually I think chronological order should be

• The good the bad and the ugly

• For a few dollars more

• A fistful of Dollars

because in a A fistful of Dollars, when Rubio is going to kill Julio we can see Eastwood's hat with bullet holes on the top in For a few dollars more Colonel Mortimer and Eastwood shoot each other's hats off