There is a street in north London lined with Paper birch trees. The thin bark is peeling of the trunks in crisp layers and if you get hold of a piece you can pull it right of in the size of a page. The bark can be separated into extremely thin, but still durable and flexible sheets, a quality that explains why it was frequently used as an early writing material. There has been hundreds of old Birch bark letters uncovered around the Novgorod area in Russia. Some of them date back as early as the 11th century. The famous mathematical Bakhshali manuscript was also written on birch bark and is believed to be from somewhere between 200 BC - 300 AD. It might be one of the earliest documents to use the concept of zero (0).