I guess "variante" means chicane in Italian, someone help e here, please. From 1954 to 1972, the circuit had no "variantes" at all. Check www.racingcircuits.net. Someone made a GP3 track with exactly that layout.
In 1973, the circuit got its first chicane: Variante Bassa, which was very similar to the old Bus Stop at Spa. But, unlike it, the first the part of it was faster the the second one. Although not as fast as Barrichello thought it could be in 1994. A lot of other circuits got their chicanes at the time: Silverstone, Monza, Zolder, Anderstorp. A year later, Variante Alta was added. That was probably when the new chicanes got their names.
The layout wasn't changed until 1981. Another chicane was made at Acqua Minerale. I have a video (I think 1990) showing Mansell during free practise just ignoring the chicane and going straight through the grass. It wasn't the first time he had done that as the grass showed proof.
The layout was changed again in 1994 because of the terrible 1994 San Marino GP. Tamburello and Villeneuve got chicanes where Senna and Ratzenberger had their fatal accidents. Rivazza was modified. But the other two alterations were interesting. Variante Bassa and Acqua Minerale became faster. Variante Bassa lost its first part and Acqua Minerale became similar to its original layout, but more challenging.
You can also see some propositons for Rivazza that were not used.