Age structure of the accreted halo components. Top: Mean age of stars accreted from the five most significant mergers as a function of galactocentric distance (R_gal) at z = 0. Bottom: Corresponding age distributions, colour-coded as above. The strongest burst of star formation is typically for the youngest stars in a given merger, thus corresponding to the time of accretion. Age estimates for accreted stars can therefore be used to time each merging event.