The Citroën DS was introduced in 1955. The DS is one of Citroën's most well known and most revered models. Widely regarded as being ahead of its time, the DS featured a sleek and futuristic design that is often considered one of the most beautiful cars ever made. The DS was offered as a sedan and station wagon, although rare and desirable convertible versions were built by coachbuilders. Among the notable innovations featured on the DS was its self levelling hydropneumatic suspension, as well as being the first mass produced car to be fitted with disc brakes. Over the course of production, the DS was built in four main variants, based on the size of their inline four engine: DS19 (1955-1968), DS21 (1965-1972), DS20 (1968-1975), and DS23 (1972-1975). These variants were also available in a variety of trim levels, including the top of the line Pallas variant. A less expensive version of the DS was sold as the Citroën ID, later the Citroën D. Production of the Citroën DS ended in 1975.