In the 1950s archeologists made a great discovery near the city of Novgorod, Russia: they dug up hundreds of pieces of birch bark with all sorts of texts written on them.
The 915 items are mostly letters, notes and receipts, all written between the 11th and 15th century. Among the more notable scraps is a marriage proposal from a man called Mikita to his beloved Anna: “marry me – I want you and you want me, and the witness to that is Ignat Moiseev”.
In the 13th century, young schoolboys learning to write filled these scraps with alphabets and short texts.
Bark was ideal material for writing down things with such a short half-life. Then the pupils got bored and started to doodle, as kids do: crude drawings of individuals with big hands, as well as a figure with a raised sword standing next to a defeated beast.
Via Erik Kwakkel with more details and additional links to further information.