Radetzky March
For the trio, Strauss used an older folk melody called "Alter Tanz aus Wien" or "Tinerl-Lied" (Tinerl was a contemporary Viennese songstress) which was originally in 3/4 time. When Radetzky came back to Vienna after winning the battle of Custoza (1848), his soldiers were singing the then-popular song. Allegedly Strauss heard this singing and incorporated the melody, converted to 2/4 time, into the "Radetzky March".