The church floor plan is a Greek cross, with he powerful central octagonal tower (64 meters tall) standing at the crossing of the four short cross arms. Externally in their corners are four square stair towers that converrt the cross plan to a near square plan.
Source Otzen, Johannes; Koch, Alexander, ed. (1895). Academy Architecture and Annual Architectual Review 1895, in English. London W.C.: Academy Architecture. p. 107.