(CNN) Monday, May 6, marks the beginning of the Muslim holy month of Ramadan .

The tradition began in the seventh century and commemorates the month when the Prophet Mohammed retreated to a cave north of Mecca for spiritual contemplation.

Each year since, Ramadan's weeks of spiritual introspection build toward Laylat al-Qadr, or the "Night of Power," believed to be the holiest night of the year, according to BeliefNet . Shia Muslims recognize it as the 23rd night of Ramadan, while the Sunni observe it on the 27th night of the month.

The Quran describes this singular evening of worship as "better than a thousand months."

It marks the day when Muslims believe the angel Gabriel began giving Mohammed revelations from God.

The Islamic calendar follows the lunar year and is therefore usually 11 days shorter than the solar year on the Gregorian calendar. Ramadan ends on June 4. The month of Ramadan begins with the new moon.

It shifts 11 days earlier each year. It takes 33 years for Ramadan to cycle back again to the same time in the Gregorian calendar.

History of revelation and conquest

Islam stems from the Judeo-Christian tradition, and holds that other holy texts including the Torah, the Psalms, and the Gospels were revealed during previous months of Ramadan.

Besides being the month of revelation, Ramadan bears other historical importance as well.

During that month in 624, Muslims won the Battle of Badr, marking their first major victory against enemies who occupied Mecca, the city where Mohammed was born.

Later, in the year 630, Mohammed led the conquest of Mecca during Ramadan, according to The New Arab. And Muslim armies won other key battles over the centuries during Ramadan.

Shiite Muslim worshippers take part in the early morning prayers for Eid al-Fitr after the conclusion of the holy fasting month of Ramadan.

A time of spiritual purification

Over the 30 days, Muslims fast during the daylight hours, and the practice is seen as one of the five pillars of the faith. They can eat before sunrise and break their fast after dusk each day, and besides abstinence from food and water, Muslims are asked to abstain from sexual intercourse as well, the Mosque Foundation says

During the month, Muslims also strive to practice "zakat," or charity, another of the five pillars of Islam.

The Arabic etymology of Ramadan references extreme heat. Fasting therefore becomes the spiritual process of burning away sin with good deeds.

The last of day of Ramadan is Eid al-Fitr, which is celebrated with feasting.