Yes they are a solid, the rings of Saturn are made up of multiple solid materials, ice and some rocky substances. They range from millimetres to meters thick.
Galileo first discovered Saturn in 1610, when he saw it the first time it was directly side on to him. But a few years later he looked again, this time at a different angle and discovered the rings.
In 1610, the year after Galileo Galilei first looked into space he became the very first person to observe Saturn's rings, though he could not see them well enough to see their true beauty. In 1655, Christiaan Huygens was the first person to describe them as a disk surrounding Saturn.