Honegger always remained in touch with Switzerland, his parents' country of origin, until the outbreak of the war and the invasion of the Nazis made it impossible for him to leave Paris. He joined the French Resistance and was generally unaffected by the Nazis themselves, who allowed him to continue his work without too much interference. He also taught composition at the École Normale de Musique de Paris, where his students included Yves Ramette. However, he was greatly depressed by the war. Between its outbreak and his death, he wrote his last four symphonies (numbers two to five) which are among the most powerful symphonic works of the 20th century. Of these, the second, for strings, featuring a solo trumpet which plays a chorale tune in the style of Bach in the final movement, and the third, subtitled "Symphonie Liturgique" with three movements that evoke the Requiem Mass (Dies irae, De profundis clamavi and Dona nobis pacem), are probably the best known. Written in 1946 just after the end of the war, it has parallels with Benjamin Britten's "Sinfonia da Requiem" of 1940. In contrast with this work is the lyrical, nostalgic Symphony No. 4, subtitled "Deliciae Basilienses" ("The Delights of Basel"), written as a tribute to days of relaxation spent in that Swiss city during the war.