  An $\mathcal{F}$-essential subgroup is called a pearl if it is either
elementary abelian of order $p^2$ or non-abelian of order $p^3$. In this paper
we start the investigation of fusion systems containing pearls: we determine a
bound for the order of $p$-groups containing pearls and we classify the
saturated fusion systems on $p$-groups containing pearls and having sectional
rank at most $4$.
