Anaerobic Archives
The survival of over 1,100 delicate birch bark documents in Veliky Novgorod is because of the local soil chemistry. The city is built on thick, waterlogged clay soil with a low oxygen content. This anaerobic environment is hostile to the microorganisms that typically decompose organic materials like wood and bark. The cultural layers of Novgorod, in some places up to eight meters (25 feet) deep, effectively sealed the discarded letters away from oxygen, preserving them for centuries. The first letter was discovered by accident on July 26, 1951, by Nina Fedorovna Akulova during an archaeological expedition led by Artemiy Artsikhovsky. Since then, finds have dated from the 11th to the 15th centuries.
The letters were not written with ink, which would have washed away, but were scratched into the soft inner surface of the bark. The tool for this was a stylus, called a "pisalo," made of iron, bronze, or bone. The writing material was cheap and readily available, unlike expensive parchment which was reserved for official and religious texts. These were disposable, everyday documents, thrown away after being read, which makes their preservation purely an accident of geology.