With nearly two billion followers, Islam originated in Arabia and spread throughout the world, becoming the world’s second largest religion after Christianity. While Mecca is its holiest site, there are other major Muslim sites—gilded mosques, mosaic-embedded shrines, and holy cities—that not only are architectural gems but provide intriguing insights into Islam’s history and culture. Here’s a look at five of Islam’s most important sites, each one a stunning icon of the faith.

1. Mecca, Saudi Arabia

Of course, Mecca tops the list. This most holy city was the birthplace of Muhammad, around A.D. 570, but it was sacred even before he came along. Adam and Abraham, potent figures from the Abrahamic traditions, have strong links to the city. Abraham’s life, in particular, was a series of trials of his faith in God, and these inspire some of the ceremonies that Muslims perform during the hajj (pilgrimage), such as sacrificing an animal and sharing the meat with the poor.

The city’s centerpiece is an ancient granite cube, the Kaaba, standing within the Holy Mosque (Masjid al-Haram) and covered by the kiswa, a black cloth woven with verses from the Quran. Muslims across the globe bow in prayer toward the Kaaba five times daily, a ritual set by Muhammad in 624.

Muslims with the means and ability are expected to visit Mecca once in a lifetime for the hajj, known as the fifth pillar of Islam. They begin and end the hajj by walking around the Kaaba seven times.

2. Medina, Saudi Arabia

As the burial place of Muhammad and the city where the Prophet and his followers fled from attacks in Mecca, Medina—about 200 miles north of Mecca—is the second holiest site in Islam. Millions of Muslims visit each year to pray at the Prophet’s Mosque (Masjid an-Nabawi). Although neither a part of the hajj nor a duty for Muslims, this act is said to be worth more than a thousand prayers at any other mosque.

Most of the current mosque, a two-tiered structure with 27 domes and an open-air courtyard, dates from the 19th and 20th centuries. Muhammad, who built the original and died in 632, lies buried under the green central dome, along with the first two caliphs, Abu Bakr and Umar. Much expanded, the mosque can now hold more than a million worshippers, with more expansion plans under way. In addition, the mosque incorporates modern technology, such as retractable Teflon umbrellas, to counter the blasting summer heat.

The Great Mosque has stood at the heart of Arab-Muslim worship for more than a thousand years. A popular saying is that if you cannot go to Mecca, seven pilgrimages to Kairouan might save your soul.

Started in A.D. 670, only 38 years after the death of the Prophet Muhammad, it was rebuilt and enlarged over the next century. The present structure is part of an expansive complex in this holy city and dates from the reign of the Arab-Muslim Aghlabid dynasty, which ruled in the Ifriqiyah region (present-day Tunisia and eastern Algeria) during the ninth century. With its buttressed walls and three-tiered minaret—the world’s oldest surviving minaret, festooned with battlements and arrow slits—the mosque was both fortress and spiritual center. Imams preached, men studied, and in time of siege, the populace took refuge here.

At the mosque’s center lies a dazzling white courtyard, enclosed on three sides by cloisters and columns. Exquisite marquetry covers the doors leading to the prayer room, accessible only to Muslim men. Inside is the minbar, or imam’s pulpit, thought to be the oldest surviving in the Islamic world; the mosaic-covered mihrab, a niche pointing in the direction of Mecca; and 17 naves supported by carved columns.

4. Harem al-Sharif, Jerusalem, Israel

Jews and Muslims both hold sacred the flat, elevated plaza atop Mount Moriah in the heart of Old Jerusalem. Consider the holiest site in Judaism, the Temple Mount is the the site of the demolished First and Second Temples that in biblical times served as a central place of worship for Israelites and Jews; only the Western Wall survives the Roman destruction of the Second Temple in 70 B.C.

After the Muslim conquest of Jerusalem in A.D. 638, the ruling caliph built the shrine of the Dome of the Rock on the Mount Moriah site, which is known to Muslims as Harem al-Sharif (Noble Sanctuary). It’s a beautiful structure, adorned with faience, marble, and mosaics, and its glittering gold-leaf roof forms the city’s most striking landmark to this day. At its heart is an outcrop of jagged rock where Muslims believe Muhammad ascended to heaven.

The Muslims built other structures, fountains, and gardens that sprinkle the 35-plus-acre Noble Sanctuary compound, including the silver-domed Al Aqsa Mosque, just south of the Dome of the Rock. One of the world’s largest mosques—more than 4,000 Muslims can prostrate themselves on the floor during prayer— it features the Isra, an Islamic tale of Muhammad’s Night Journey. According to this story, Muhammad is said to have traveled from Mecca to the Al Aqsa Mosque on the back of the Buraq, a winged horse-like creature, to lead other prophets in prayer.

5. Umayyad Mosque, Damascus, Syria

Al-Walīd I, the caliph who built the Umayyad Mosque circa A.D. 715, famously proclaimed: “People of Damascus, four things give you a marked superiority over the rest of the world: your climate, your water, your fruits, and your baths. To these I add a fifth: this mosque.”

The mosque, also known as the Great Mosque of Damascus, stands on the site of a succession of places of worship, including a Roman temple and a Christian church. It centers on a great central courtyard surrounded by an arcade of arches, with the prayer hall covering the southern side. Within the prayer hall, an ornate domed shrine of deep green glass is believed to contain the head of St. John the Baptist, a Jewish prophet who baptized Jesus and is known to Muslims as the prophet Yahya. This part of the mosque is sacred to both Christians and Muslims. Also contained within the mosque is a shrine believed to contain the head of Hussein ibn Ali, Muhammad’s grandson whose martyrdom is frequently compared to those of John the Baptist and Jesus.