Prohibition of free traffic during the Edo period added to the differentiation of dialects that were already numerous because of geological isolation and some dialects sounded like nanbangekizetsu (foreign language) between people in different domains.
「江戸時代の自由交通厳禁のために、地形上すでにあまたの方言があったところへさらに拍車がかかり、他藩人相互間では南蛮鴃舌(なんばんげきぜつ)としか聞こえない方言が多くなった。