A fifth of humankind follows Islam, the fastest growing and perhaps most misunderstood religion on earth. Faced with a secular modern world, Muslims are turning anew to the roots of their faith.

Borne aloft five times a day, from Shanghai to Chicago, Jakarta to Timbuktu, Islam's call to prayer stirs the soul of devout Muslims everywhere. Whether cast from metal loudspeakers over teeming city streets or lifted as the murmured song of camel drivers kneeling in the sand, it begins with the same Arabic phrase Muslims have used for nearly 1400 years, Islam's melodic paean to the Creator: "Allahu Akbar -- God is Great."

Some 1.3 billion human beings -- one person in five -- heed Islam's call in the modern world, embracing the religion at a rate that makes it the fastest growing on Earth, with 80 percent of believers now outside the Arab world.

The term Islam, is an Arabic word meaning "submission to God," with its etymological roots firmly planted in "salaam", or peace.

Muslims revere all Prophets of God, including Moses and Jesus, may Allah exalt their mention, and regard the books revealed to these prophets – Torah and Injeel -- as an integral part of their tradition. They disagree with Christians about the divinity of Jesus, may Allah exalt his mention, but honor him as an especially esteemed Messenger from God. The ultimate Messenger for Muslims is the Prophet Muhammad (may Allah exalt his mention).

Born about 570 CE at Makkah, Muhammad was an orphan raised by his grandfather and uncle. He grew up to be a modest and respected businessman who rejected the widespread polytheism of his day and turned to the One God.

At about age 40, Muhammad retreated to a cave in the mountains outside Makkah to meditate. There, he was visited by the archangel Gabriel, who began reciting to him the Word of God. Until his death 23 years later, Muhammad passed along these revelations to a growing band of followers, including many who wrote down the words or committed them to memory.

These verses became the Quran, or "recitation," the literal Word of God and confirmation of the real Jewish and Christian Scriptures.

The Quran consists of 114 chapters, and covers everything from the nature of God (Compassionate and Merciful) to laws governing the mundane affairs of men. Among its commands are (what mean): "Do not usurp one another's property by unjust means" and "Do not kill anyone which God has forbidden."

The Quran is also a source of the pure Arabic language memorized by Muslim school children and recited by Muslim adults on every important occasion.

One of the five pillars of Islam, along with the two testimonies of faith (Shahaadah), prayer (Salah), fasting the month of Ramadan (Sawm), charity (Zakah), the pilgrimage (Hajj) is required of all who can manage it at least once in a lifetime.

By the time the Prophet passed away in 632 CE, Islam was established throughout the Arabian Peninsula, bringing peace and unity to the tribes for the first time in memory. Within a century of his death the armies of Islam, empowered by faith, had conquered a vast swathe of territory -- stretching from India to the Atlantic coasts of Spain and Portugal, including North Africa and the Middle East.

This Islamic world built on the intellectual achievements of other civilizations, sponsoring an explosion of learning unparalleled until the Renaissance.

At a time when Europe was languishing in the early Middle Ages, Muslim scholars and thinkers were giving the world a great center of Islamic learning (Al-Azhar in Cairo) and refining everything -- from architecture to the use of numbers. At the same time, seagoing Muslim traders were spreading the faith to southern Asia, China and the east coast of Africa.

Flourishing by the end of the first millennium, the realm of Islam was tested as western Europe, spurred by its contact with the Islamic near East, awoke and lashed out, launching a series of armed Crusades to wrest Jerusalem from Muslim control.

Though fragmented and initially overcome, Muslims rallied to ultimately defeat the invading Christian armies, whose blood-soaked legacy -- the indiscriminate killing of thousands of innocent Muslim and Christian Arabs, and the Jews of Jerusalem -- lives on in the minds of people to this day.

As Europe rose to glory during the Renaissance and beyond, the Islamic world continued to thrive after the creation of the Ottoman Empire in the late 1200s CE. This powerful state fell at the end of World War I, resulting in the subdivision of its mostly Muslim lands into the Middle Eastern countries we know today.

Although a few Muslim nations are wealthy from oil resources, most are poor and increasingly demoralized by their position in the world. Disaffected and disenfranchised, many people in these societies are turning to Islam to assert their identity and reclaim power over their own lives.

In addition many Muslims, especially in the Arab world, are angry at the United States’ continued support of Israel, the war and the economic sanctions against ‘Iraq, which are widely perceived to have hit the people of ‘Iraq -- who are fellow Muslims -- right between the eyes.

For most of the world's 1.3 billion Muslims, Islam is a way of life, a discipline based on looking at the world through the eyes of faith.

"Islam gave me something that was lacking in my life," says Jennifer Calvo of Washington, DC.

Calvo is 28 and looks as if she just stepped out of a painting by Botticelli, with aquiline features and striking blue eyes, set off by a white head scarf tucked neatly into her full-length robe. Calvo was raised Catholic and works as a registered nurse.

Two years ago, as people have done for 1,400 years, Jennifer became a Muslim by simply declaring the words: "Laa ilaaha illallaah, Muhammad Rasoolullaah” (There is none worthy of being worshipped except Allah (God), and Muhammad is His Messenger)."

"Everything is so much simpler now," she said. "It's just me and God. For the first time in my life I'm at peace."

For Calvo and most Muslims on Earth, that is what Islam's call to prayer represents. Kneeling to God five times a day, in unison, facing Makkah from wherever they happen to be, they find peace in an act of surrender.