National Azulejo Day is observed in Portugal on May 6 each year, celebrating the significance of azulejos, a form of Portuguese tin-glazed ceramic tilework that is integral to Portuguese architecture. The term "azulejo" is derived from the Arabic word "zellij," reflecting its historical roots in medieval Moorish architecture. Azulejos were introduced to Portugal in the early 16th century after being developed in Seville around the 13th century. The Golden Age of the Azulejo occurred in the late 17th and early 18th centuries, during which these tiles adorned churches, palaces, and homes. Significant locations for azulejos include the Palace of Sintra, a UNESCO World Heritage Site, and the National Museum of the Azulejo in Lisbon. However, azulejos face threats from neglect and theft, prompting initiatives like the SOS Azulejo Project, launched in 2007, to protect and preserve these cultural treasures.