Timeline of the formation of clusters in Sco-Cen, color-coded by age (same as in Fig. 1) and scaled by cluster size. The horizontal lines represent age uncertainties. While Sco-Cen has been forming small clusters (≤250 stars) continuously since its formation 20–25 Myr ago, its large clusters (≳1000 stars) were all formed during the peak of the star formation rate, around 15 Myr ago. Regarding their absolute numbers, most of the stars and clusters we can observe today in the Sco-Cen region were formed around 15 Myr ago. Since then, star formation has been declining. The peaks of star and cluster formation rate seem to be periodically distributed (every ∼5 Myr, see also Fig. 3).