In the 1790s Goya became ill. It is not known exactly what his illness was. It is believed that he suffered mental breakdown. He may have had viral encephalitis or several strokes. He may have suffered from dementia. It is also thought that he may have been poisoned by lead paint. His sight, hearing, balance and mental health were all affected. From the 1790s onwards he began to paint pictures showing sad, violent subjects. His unhappiness was also affected by the French invasion of Spain in 1808. One of his most famous paintings, "The Third of May 1808", is about the execution of Spanish men trying to defend their country.