The Ordovician was named by the British geologist Charles Lapworth in 1879. He took the name from an ancient Celtic tribe, the Ordovices, renowned for its resistance to Roman domination. For decades, the epochs and series of the Ordovician each had a type location in Britain, where their characteristic faunas could be found, but in recent years, the stratigraphy of the Ordovician has been completely reworked. Graptolites, extinct planktonic organisms, have been and still are used to correlate Ordovician strata.
