"Europe" as a cultural concept is substantially derived from the shared heritage of the Roman Empire and its culture. The boundaries of Europe were historically understood as those of Christendom (or more specifically Latin Christendom), as established or defended throughout the medieval and early modern history of Europe, especially against Islam, as in the Reconquista and the Ottoman wars in Europe This shared cultural heritage is combined by overlapping indigenous national cultures and folklores, roughly divided into Slavic, Latin (Romance) and Germanic, but with several components not part of either of these group (notably Greek and Celtic). Cultural contact and mixtures characterise much of European regional cultures; Kaplan (2014) describes Europe as "embracing maximum cultural diversity at minimal geographical distances."