Since swimming was done in a state of undress, it became less popular as society became more conservative in the early Modern period. Leonardo da Vinci made early sketches of lifebelts . In 1538, Nikolaus Wynmann, a Swiss–German professor of languages, wrote the earliest known complete book about swimming, Colymbetes, sive de arte natandi dialogus et festivus et iucundus lectu ( The Swimmer, or A Dialogue on the Art of Swimming and Joyful and Pleasant to Read ). His purpose was to reduce the dangers of drowning . The book contained a good methodical approach to learning breaststroke, and mentioned swimming aids such as air filled cow bladders , reed bundles, and cork belts. In 1587, Everard Digby also wrote a swimming book, claiming that humans could swim better than fish. Digby was a Senior Fellow at St. John's College, Cambridge and was interested in the scientific method. His short treatise, De arte natandi , was written in Latin and contained over 40 woodcu...