​The Narva River constitutes an important cultural and political border between Estonia and Russia. It has also been a border between European and Slavonic cultural space since the 13th century when fortifications were built on both sides of the Narva River. The oldest survived parts of the Narva stronghold, founded by the Danes, date from the turn of the 13th and 14th centuries, the Ivangorod stronghold on the opposite shore (Jaanilinn) dates from the second half of the 15th century.