Editing Calendar-based contraceptive methods (section)

===Early methods===
It is not known if historical cultures were aware of what part of the menstrual cycle is most fertile. In the year 388, [[Augustine of Hippo]] wrote of periodic abstinence. Addressing followers of [[Manichaeism]], his former religion, he said, "Is it not you who used to counsel us to observe as much as possible the time when a woman, after her purification, is most likely to conceive, and to abstain from cohabitation at that time...?"<ref name="augustine">{{cite book |last=Saint |first=Bishop of Hippo Augustine |editor=Philip Schaff |title=A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church, Volume IV |publisher=WM. B. Eerdmans Publishing Co. |year=1887 |location=Grand Rapids, MI |chapter-url=http://www.ccel.org/ccel/schaff/npnf104.iv.v.xx.html |chapter=Chapter 18.—Of the Symbol of the Breast, and of the Shameful Mysteries of the Manichæans}}</ref>  If the Manichaieans practiced something like the Jewish [[niddah|observances of menstruation]], then the "time... after her purification" would have indeed been when "a woman... is most likely to conceive."<ref name="green">{{cite book |first=Shirley |last=Green |year=1972 |title=The Curious History of Contraception |publisher=St. Martin's Press |location=New York |isbn=0-85223-016-8 |pages=138–43}}</ref>  Over a century previously, however, the influential [[Ancient Greek medicine|Greek physician]] [[Soranus of Ephesus|Soranus]] had written that "the time directly before and after menstruation" was the most fertile part of a woman's cycle; this inaccuracy was repeated in the 6th century by the [[Byzantine]] physician [[Aëtius Amidenus|Aëtius]]. Similarly, a [[China|Chinese]] sex manual written close to the year 600 stated that only the first five days following menstruation were fertile.<ref name="green"/> Some historians believe that Augustine, too, incorrectly identified the days immediately after menstruation as the time of highest fertility.<ref name="mclaren">{{cite book |last=McLaren |first=Angus |title=A History of Contraception: From Antiquity to the Present Day |publisher=Blackwell Publishers |year=1992 |location=Oxford |page=74 |isbn=0-631-18729-4}}</ref>

Written references to a "safe period" do not appear again for over a thousand years.<ref name="green"/> Scientific advances prompted a number of secular thinkers to advocate periodic abstinence to avoid pregnancy:<ref name="wife"/> in the 1840s it was discovered that many animals ovulate during [[estrus]].  Because some animals (such as [[dog]]s) have a bloody discharge during estrus, it was assumed that menstruation was the corresponding most fertile time for women.  This inaccurate theory was popularized by physicians [[Theodor Ludwig Wilhelm Bischoff|Bischoff]], [[Félix Archimède Pouchet]], and Adam Raciborski.<ref name="green"/><ref name="mclaren"/> In 1854, an [[English people|English]] physician named George Drysdale correctly taught his patients that the days near menstruation are the ''least'' fertile, but this remained the minority view for the remainder of the 19th century.<ref name="green"/>