The C-1s core photoelectron shakeup spectrum of fullerene has been studied experimentally and theoretically, as well as the corresponding spectra of the smaller model compounds acenaphthylene and naphthalene. It is found that many of the shakeup excitations of C-60 Can be classified in terms of excitations found in the model compounds. A population analysis of the orbitals involved reveals a systematic behavior, enabling a generalization to extended aromatic systems and to an infinite graphite layer.