  Gamma-ray bursts (GRBs) are energetic explosions that for 0.01--100 s are the
brightest gamma-ray sources in the sky. Observations of the early evolution of
afterglows we expected to provide clues about the nature of the bursts, but
their rapid fading has hampered such studies; some recent rapid localizations
of bursts have improved the situation. Here we report on an early detection of
the very bright afterglow of the burst of 29 March 2003 (GRB030329). Our data
show that, even early in the aferglow phase, the light curve shows unexpectedly
complicated structures superimposed on the fading background.
