Today we're looking at two kinds of strata—not the rocky kind, but the linguistic kind. A stratum, or 'layer', describes the influence one language has on the development of another in terms of its vocabulary, grammar, syntax, or other features. Historically, linguistic changes have come about largely due to migration, when one group brings its language into the territory where another language is already in use. When the migration is the result of war or takeover, the language of the conquering group is called a superstratum, whereas the preexisting language of the region is called the substratum. Although the name substratum and the subservient position of the conquered group imply a lower status, often its language is the one that endures. In France, for example, the original Gaulish language is a substratum because it was largely superseded by Latin after the Roman conquest. Later, though, the Germanic Franks conquered France—so their Frankish language is the superstratum—but they gradually adopted the Latin of their subjects.