The late 1960s and early 1970s formed a significant epoch in the world of international sports car racing. As the motor racing rule-making body moved back and forth between cars that less and less resembled road-going vehicles, prototype sports car racing captured the imagination of manufacturers, teams and fans alike. Porsche vs Ferrari vs Alfa Romeo vs Matra provided some of the best ever racing for sports cars. At first the 5-litre Porsches and Ferraris battled through 1970 and 1971, but the 3-litre prototypes that previously had run in another class rapidly became more and more competitive.  By 1973, the Ferrari 312PB, little more than a Grand Prix car with full bodywork, was dominating the scene. This has always been viewed as one of the great eras in sports car racing, when all the Grand Prix drivers were fully active in sports cars as well as F1 machines. With 100 contemporary pictures, this is the story of a great time in motor sport history.