Conversation so far:
What is Tristan and serialism?
Messiaen composed the song cycle Harawi, the first of three works inspired by the legend of Tristan and Isolde.
What was the song about?
The second of these works about human (as opposed to divine) love was the result of a commission from Serge Koussevitzky.
Was he commissioned to write any other songs?
CANNOTANSWER.
Are there any other interesting aspects about this article?
Messiaen taught an analysis class at the Paris Conservatoire.
How long did he teach for?
In 1947 he taught (and performed with Loriod) for two weeks in Budapest.
What else did he do in Budapest?
In 1949 he taught at Tanglewood.
Did he travel any where else?
Beginning in summer 1949 he taught in the new music summer school classes at Darmstadt.
Did he teach anywhere else?
CANNOTANSWER.

Question: What else is notable about this time?
Self-contained rewrite: What else is notable about 1949 besides Olivier Messiaen teaching at Darmstadt?