Thatta is a city in the Pakistani province of Sindh. Thatta was the medieval capital of Sindh, and served as the seat of power for three successive dynasties. Its construction was ordered by Jam Nizamuddin II in 1495. Thatta's historic significance has yielded several monuments in and around the city. Thatta's Makli Necropolis, a UNESCO World Heritage Site, is site of one of the world's largest cemeteries and has numerous monumental tombs built between the 14th and 18th centuries designed in a syncretic funerary style characteristic of lower Sindh. The city's 17th century Shah Jahan Mosque is richly embellished with decorative tiles, and is considered to have the most elaborate display of tile work in the South Asia.

Thatta refers to riverside settlements. Villagers in the rural areas of lower Sindh often refer to the city as Thatta Nagar, or simply Nagar. The name of Thatta, one of the oldest towns, was derived from the Persian term Tah-Tah which literally means "layer over layer", signifying a settlement that has gone through various civilizations. Ḳāni, an 18th century scholar, gave two theories regarding the etymology of Thatta. The first theory suggests that Thatta is a distortion of ‘Teh Teh’ which refers to the migration of people from northern cities to Thatta. The second theory suggests that the name originates from thatt, the Sindhi term for a place of gathering.

Thatta may be the site of ancient Patala, the main port on the Indus in the time of Alexander the Great, though the site of Patala has been subject to much debate. Before it, Hindus called it Sarnee Nagar, but in 332 BC, Greeks first time called it Pattala or Patala then it became Nagar Tatta in Mughal Period. Muhammad bin Qasim captured the region in 711 CE after the defeating the Raja Dahir in a battle north of Thatta. Thatta is reported by some historians to have been the ancient seaport of Debal that was mentioned by the Arab conquerors, though others place the seaport at the site of modern Karachi. At the time of the Umayyad conquests, small semi-nomadic tribes were living in the Sindh region. The Umayyad conquest introduced the religion of Islam into the hitherto mostly Hindu and Buddhist region.

Following Mahmud of Ghazna's invasion of Sindh in the early 11th century, the Ghaznavids installed Abdul Razzaq as Governor of Thatta in 1026. Under the rule of the Ghaznavids the local chieftain Ibn Sumar, then ruler of Multan, seized power in Sindh and founded the Sumra dynasty, which ruled from Thatta from 1051 for the next 300 years. Under Sumra rule, Thatta's Ismaili Shia population was granted special protection. The Sumra dynasty began to decline in power by the 13th century, though Thatta and the Indus Delta remained their last bastions of power until the mid 14th century.

In 1351, the Samma Dynasty, of Rajput descent from Sehwan, seized the city and made it their capital as well. It was during this time that the Makli Necropolis rose to prominence as a funerary site. Muhammad bin Tughluq died in 1351 during a campaign to capture Thatta. Firuz Shah Tughlaq unsuccessfully attempted to subjugate Thatta twice; once in 1361 and again in 1365.

In 1520, the Samma ruler Jam Feroz was defeated by Shah Beg of the Arghun-Tarkhun dynasty, which in turn had been displaced from Afghanistan by the expanding Timurid Empire in Central Asia. The Tarkhuns fell into disarray in the mid-1500s, prompting Muhammad Isa Tarkhun (Mirza Isa Khan I) to seek aid from the Portuguese in 1555. 700 Portuguese soldiers arrived in 28 ships to determine, at the time of their arrival, that Isa Tarkhun had already emerged victorious from the conflict. After the Tarkhuns refused to pay the Portuguese soldiers, the Portuguese plundered the town, robbing its enormous gold treasury, and killing many inhabitants. Despite the 1557 Sack of Thatta, the 16th century Portuguese historian Diogo do Couto described Thatta as one of the richest cities of the Orient.

Nevertheless, some Portuguese presence was early in the 16th century with the conquest of Hormuz by Afonso de Albuquerque in 1507, which started the relationship with Sindi. Later in the first decade of the 16th century, traders created a factory (feitoria), and at the end of the 16th century a religious Order (Carmelitas Descalços) Secular Order of Discalced Carmelites a convent.

The city was destroyed by Mirza Jani Beg in the 16th century. Beginning in 1592 during the reign of Emperor Akbar, Thatta was governed by the Mughal Empire based in Agra, which lead to a decline in the city's prosperity as some trade was shifted towards other Mughal ports.