The new monarch pursued an independent policy: after stopping a Frankish attack in 855, he also sought to weaken influence of Frankish priests preaching in his realm.
Rastislav asked the Byzantine Emperor Michael III to send teachers who would interpret Christianity in the Slavic vernacular.
The political and cultural development in Slovakia continued in two separate lines.
Similarly to his predecessor, Svätopluk I (871–894) assumed the title of the king (rex).During his reign, the Great Moravian Empire reached its greatest territorial extent, when not only present-day Moravia and Slovakia but also present-day northern and central Hungary, Lower Austria, Bohemia, Silesia, Lusatia, southern Poland and northern Serbia belonged to the empire, but the exact borders of his domains are still disputed by modern authors.The Slavs in southern Slovakia adopted new burial rite (inhumation), jewelry, fashion and used also common cemeteries with the Avars.Large Slavo-Avaric cemeteries can be found in Devínska Nová Ves and Záhorská Bystrica near Bratislava and similar cemeteries, the proof of direct Avar power, south of the line Devín-Nitra-Levice-Želovce-Košice-Šebastovce.In this time, the Avars already began to adopt a more settled lifestyle.
The new period introduced Slavo-Avaric symbiosis and multi-ethnic Slavo-Avaric culture.
Neolithic habitation was found in Želiezovce, Gemer, and the Bukové hory massif, the Domica cave, and at Nitriansky Hrádok.
Bronze Age was marked by the Čakany and Velatice cultures, and then the Lusatian culture, followed by the Calenderberg culture and the Hallstatt culture.
The Avars held strategic centers in Devín and Komárno which belonged to the most important centers of the khaganate.
The Avars from Devín controlled Moravia and from Komárno they controlled southern Slovakia.
He also writes that the Slavs, who remained "an independent third party" in strained Longobard-Gepid relations, were not interested in conflicts with their Germanic neighbours, but made raids in the faraway Byzantine Empire. Barford, these features suggest that the Carpathian Mountains and the Sudetes separated the ancestors of the Slovaks and the Czechs from the Slavs living to the north of those mountains.