1956 Maserati 450S Prototype by FantuzziRM Auctions has some very special and expensive Italian sportscars of the 50s and 60s consigned for its auction in Monaco on May 10, but the one that currently carries the highest estimated value at between 4 and 5.5 million euros ($5.5 - $7.5 million) is a 1956 Maserati 450S with some very interesting provenance.

The Maserati started its life as a six-cylinder 350S that Stirling Moss drove in the 1956 Mille Miglia race. Unfortunately, the brakes failed, and it crashed into a tree and nearly into a ravine. Moss and his co-driver weren't injured, but the car was kaputt.

Maserati repaired it and used the chassis as a test mule for its new 5.7-liter V8 racecar called the 450S. It featured an extended wheelbase to fit the larger engine and a new body with a single seat. The racer hit the track again at the hands of Moss and Juan Manuel Fangio in the 1957 Buenos Aires 1000 KM but retired with transmission issues. Later that season, it crashed again at the 1957 Mille Miglia at the hands of driver Jean Behra. After that, the car sat around the workshop until it was sold without an engine in 1965.

After kicking around several owners, the 450S received a restoration in the 80s with a correct V8 engine being installed, and it made its grand reemergence in the 1987 Mille Miglia. According to RM, it has mostly sat on display in a climate-controlled environment since then.

The 450S is a rarity, with Maserati only building 11 of them, counting the prototype. While the test car proved temperamental on the track, the other cars won at Sebring and the Swedish Grand Prix in 1957.