  We report the discovery of a population of Wolf-Rayet stars in the young
Galactic open cluster Westerlund 1. In an incomplete shallow spectroscopic
survey, we find six nitrogen-rich (WN) and five carbon-rich (WC) WR stars. We
also confirm the presence of a large population of yellow supergiants, some of
which are candidate hypergiants. Given this population, Westerlund 1 is likely
to be one of the most massive young clusters in the Local Group.
