This article is about the M1 and T4 lines. For the M2 line, see the article M2.

The Istanbul LRT (Hafif raylı sistem or Hafif Metro (Light Metro) in Turkish), which consists of the M1 and T4 lines, is a light metro system in Istanbul with a total length of 32 km (10.4 km underground). There are 36 stations, including 12 underground and 3 viaduct stations. The lines are totally segregated from other traffic, without level crossings. 114 train sets transport 320,000 passengers a day. The investment cost US$ 700 million.

The first line began service on September 3, 1989, between Aksaray and Kartaltepe. On December 18, 1989, the line was extended to Esenler, but at that time the Otogar (Intercity Bus Station) was omitted. The Otogar station was opened on January 31, 1994. Following this, the Terazidere, Davutpaşa, Merter, Zeytinburnu and Bakırköy stations were opened in the same year. Ataköy (Şirinevler) and Yenibosna stations were opened in 1995, when the length of the line reached approximately 16 km. In 1999, a station between Atatköy and Bakırköy, the Bahçelievler station, was opened. Finally, the line was completed on December 20, 2002, through an extension to the World Trade Center and Atatürk Airport in Yeşilköy.

Istanbul (Turkish: İstanbul) is the largest city in Turkey, forming the country's economic, cultural, and historical heart. With a population of 13.4 million, the city is at the center of the second-largest urban area in Europe after Moscow, and among the world's largest cities by population within city limits. Istanbul's vast area of 5,343 square kilometers (2,063 sq mi) is coterminous with Istanbul Province, of which the city is considered capital. Straddling the Bosphorus—one of the world's busiest waterways—in northwestern Turkey, between the Sea of Marmara and the Black Sea, Istanbul is a transcontinental city, with one third of its population living in Asia but its commercial and historical center in Europe.

Founded around 660 BC as Byzantium on the Seraglio Point, the city now known as Istanbul developed to become one of the most significant cities in history. For nearly sixteen centuries following its reestablishment as Constantinople in 330 AD, it served as the capital of four empires — the late classical Roman Empire (330–395), the Eastern Roman ("Byzantine") Empire (395–1204 and 1261–1453), the Latin Empire (1204–1261), and the Ottoman Empire (1453–1922). It was instrumental in the advancement of Christianity during Roman and Byzantine times, before the Ottomans conquered the city in 1453 and transformed it into an Islamic stronghold from which the last caliphate ruled. Although the Republic of Turkey established its capital elsewhere, in Ankara, remnants of Istanbul's previous central role still remain highly visible across the city, with palaces and imperial mosques lining its hills.

Yan Yan was a general of Shu Han during the late Han Dynasty and Three Kingdoms period of Chinese history. Yan began his career as a general serving under the warlord Liu Zhang of Yi Province.

In Luo Guanzhong's historical novel Romance of the Three Kingdoms, Yan Yan was defeated captured by Zhang Fei in 212 in one of the battles during Liu Bei's takeover of Yi Province. Yan firmly refused to surrender and made strong accusations at Liu Bei, which angered Zhang Fei. Zhang wanted to have him executed but changed his mind later as he was impressed with Yan's strong sense of loyalty. Zhang released Yan and succeeded in persuading Yan to join Liu Bei's forces.

Yan appeared in a later chapter during the Battle of Mount Dingjun, where he volunteered to lead an army to attack the enemy forces under Cao Cao together with Huang Zhong.