Muslims around the world are preparing to celebrate the beginning of Ramadan, a month-long period of religious reflection and devotion.

Ramadan marks the month the Prophet Mohammed is believed to have had the holy book, the Koran, revealed to him by God.

The holy month is observed by a large proportion of the world's estimated 1 billion Muslims, and has been observed for centuries in roughly the same way.

It occurs during the ninth month in the lunar calendar, which is different from the internationally-recognised solar calendar.

Muslims cannot eat and drink at all in the daytime during this period, breaking their fast when the sun sets and eating again before the sun rises.

Practising piety

They are expected to spend much of their day in prayer and reflection, during which they learn how life can be a mixture of body and soul - of spiritual faith and the reality of life.

It is regarded by many as a month-long exercise in practising how to be a pious, religious person throughout the rest of the year.

The number of worshippers making pilgrimages to two of Islam's holiest sites, Mecca and Medina in Saudi Arabia, increases during Ramadan - especially during the last 10 days.

But the holy month is also a social occasion, which has developed over time into a festival.

After sunset, families break their fasts by sharing festive meals of special Ramadan treats, such as Konafa, an Egyptian dessert made of shredded wheat and syrup, or Katayef, sweets stuffed with nuts, which are a popular dessert among Palestinians.

But most important are dates, which, according to Islamic teachings, were eaten by Prophet Mohammed at the end of each day of the fasting month. These are seen as a spiritual reminder of the reason behind the fasting and feasting.

Lighting up Ramadan

Many Muslim countries change their hours of business during Ramadan, and this year in Egypt, the government has gone one step further and declared an additional day off every week to make the lives of workers easier.

The streets of the Egyptian capital Cairo are currently alight with special festive lanterns. These have been used to light up Ramadan nights there since the Fatimids - a North African Shiite Moslem dynasty, which ruled Egypt from 969 to 1171.

Nowadays, the lamps are mainly used for decoration and children's toys.

And since Christmas has fallen at the same time as Ramadan for two years in a row, shops and hotels in some countries - such as Egypt and Lebanon - have decorated their trees with garlands of lanterns, to join the two traditions.

The fast will last for 29 or 30 days, depending on when the first moon of Ramadan is sighted, and will end with the celebration of Eid al-Fitr (festival of the breaking of the fast), during which, some governments grant amnesties to political and other prisoners.