The Baska Tablet, ca 1100. Two meters long, and 800 kg. Written in Croatian Glagolitic. Read more here. Pic via.
Music in Croatian glagolitic, 1600s. More pics & info here.
Slavic Glagolitic character, thanks to Submarine @sinkdeep for pointing it out! The Glagolitic alphabet is the oldest known Slavic alphabet from the 9th century.