Adha, a period of "communal enjoyment" for Muslims worldwide, has officially arrived. Here's what we've learned about the Islamic holiday.

The Hajj leading up to Eid al-Adha is one of the five pillars of Islam. The pilgrimage is one of the largest religious gatherings in the world. Mecca, considered the holiest city in Islam, is the site of Muhammad’s first revelation of the Quran.

Under the damaged dome of al-Albani Mosque in Khan Younis, families stood on broken stone and dust, raising their voices in takbir, the declaration of god's greatness, to mark the first morning of Eid al-Adha on Friday.