In the late 9th to early 10th century, the Persian physician Muhammad ibn Zakariya al-Razi documented coitus interruptus, preventing ejaculation and the use of pessaries to block the cervix as birth control methods. He described a number of pessaries, including elephant dung, cabbages and pitch, used alone or in combination.[9] During the same period Ali ibn Abbas al-Majusi documented the use of pessaries made of rock salt for women for whom pregnancy may be dangerous. In the early 10th century the Persian Polymath Abu Ali al-Hussain ibn Abdallah ibn Sina, known in Europe as Avicenna, included a chapter on birth control in his medical encyclopedia The Canon of Medicine, listing 20 different methods of preventing conception.[8]