The Chellah or Shalla (Berber languages: Sla or Calla; Arabic: شالة), is a medieval fortified Muslim necropolis and ancient archeological site in Rabat, Morocco, located on the south (left) side of the Bou Regreg estuary. The earliest evidence of the site's occupation suggests that the Phoenicians established a trading emporium here in the first millennium BC. This was later the site of Sala Colonia, an ancient Roman colony in the province of Mauretania Tingitana, before it was abandoned in Late Antiquity. In the late 13th century the site began to be used as a dynastic necropolis for the Marinid dynasty. By the mid-14th century Marinid sultans had enclosed a part of the site with a new set of walls and built a religious complex inside it to accompany their mausoleums. In the 15th century the necropolis began to decline and it suffered damage over the centuries due to earthquakes and looting. Archeological excavations in the 20th century unearthed the remains of the ancient Roman town. Today the site is a tourist attraction and since 2012 it forms part of a UNESCO World Heritage Site.

The Phoenicians founded several trading colonies along the Atlantic coast of what is now Morocco, but the existence of a Phoenician settlement on the site of Chellah has been debated by archeologists. Jean Boube, who led some of the modern excavations at the site, discovered neo-Punic artifacts dating as far back as the 3rd century BC, which suggests there must have been a small trading post here around that time. Later excavations by Boube also found fragments of Phoenician or Punic bowls dating to the 7th and early 6th centuries BC, but it is possible that such early items were imported by trade rather than being evidence of occupation. The settlement along the banks of the Bou Regreg was known as Shalat (Punic: 𐤔𐤏‬𐤋𐤕, šʿlt; compare Hebrew סלע, rock), which appears to derive from the Punic word for "rock".

By the first century BC the local inhabitants were still writing in the neo-Punic language but the region came under the influence of Rome. At this time the area was occupied by the ancient Berber Mauretanian Kingdom. Under its last two rulers, Juba II and Ptolemy, the Mauretanian kingdom became a client state of Rome. Some relics from the time of these two kings have been discovered at Chellah. After the death of Ptolemy in 40 AD the region was annexed by Rome and became the province of Mauretania Tingitana.

On this site the Romans built their own city, Sala Colonia. The Roman town was referred to as "Sala" by Ptolemy, a 2nd-century writer. Excavations have revealed that older Mauretanian structures existed on the site before Roman structures were built over them. For the Roman period, they show a substantial port city with ruined Roman architectural elements including a decumanus maximus or principal roadway, a forum and a triumphal arch. The area around the forum, excavated and visible today, was subjected to many transformations over time and the exact chronology of these is still debated. Inscriptions found on site show that the city had the status of a municipium around the mid-2nd century AD.

One of the two main Roman roads in Mauretania Tingitana reached the Atlantic through Iulia Constantia Zilil (Asilah), Lixus (Larache) and Sala Colonia. Another may have been built towards the south, from Sala to modern Casablanca, then called Anfa. The Romans had two main naval outposts on the Atlantic coast of the province: Sala Colonia, and Lixus. The port of Sala (now disappeared) was used by commercial Roman ships as a way station on their southwestward passages to Anfa and the Insula Purpuraria (Mogador island).

Sala remained linked to the Roman Empire even after the withdrawal in the 4th century of the occupying Roman legions to Tingis (Tangier) and Septem (Ceuta) in northern Mauretania Tingitana. A Roman military unit remained there until the end of the 5th century. Some of the major monuments of the town were abandoned around this time. The site of the large capitolium temple, for example, was turned into a cemetery and a dumping ground during the 4th century. Archaeological objects of Visigothic and Byzantine origin found in the area attest to the persistence of commercial or political contacts between Sala and Roman Europe, up to the establishment of a Byzantine presence in North Africa during the 7th century. Fragments of pottery with Christian motifs and graffiti have also been found among objects dating from the 4th to 6th centuries.

Sala began to be abandoned in the 5th century and was mostly in ruins when the Muslim Arabs arrived in the 7th century. The Byzantine governor of the area, Count Julian of Ceuta, surrendered to Uqba ibn Nafi in 683.

The area was only occupied again in the 10th century, when historical sources mention the existence of a ribat in the area. Around 1030, a new town called Salā (present-day Salé) was founded on the opposite side of the river (the north side) by the Banu 'Ashara family. After the end of the Umayyad Caliphate in Al-Andalus in the early 11th century, the Almoravids assumed control of the region and built a new ribat at the mouth of the river. This ribat was in turn destroyed and then rebuilt by their successors, the Almohads, in the mid-12th century, becoming what is now known as the Kasbah of the Udayas. The Almohad caliph Abu Yusuf Ya'qub al-Mansur (r. 1184–1199) also began construction of a vast new royal city with new walls on the site next to ancient Sala, corresponding to what is now the historic center of Rabat, but it was never finished. The town of Salā on the right bank (northern side) of the river continued to develop and during the following Marinid dynasty period (13th to 15th centuries) it grew more important than the settlements of the left bank.

During the Marinid period the site of ancient Sala was re-appropriated and turned into a royal necropolis for the ruling dynasty, now known as Chellah (Arabic: شالة, romanized: Shāllah). Because of its ruined condition today, the exact chronology of its development is not well known. The first Marinid constructions and the first royal burial were in 1284–85, when sultan Abu Yusuf Ya'qub chose the site to bury his wife, Umm al-'Izz. He built a small mosque (still extant) next to her tomb. The tomb itself was a qubba, a small mausoleum chamber covered by a dome or pyramidal roof. The sultan himself was buried next to her after his death in Algeciras in 1286. His son and successor, Abu Ya'qub Yusuf, was buried at the site after his death in 1307, and his successor, Abu Thabit 'Amir, was buried near Abu Ya'qub Yusuf in 1308.

The most important Marinid constructions appear to have occurred during the reigns of Abu Sa'id Uthman II (r. 1310–1331) and his son, Abu al-Hasan (r. 1331–1348; also known as the Black Sultan). Abu Sa'id enclosed the area with a set of walls and began construction of the main gate. According to some sources he was buried in this necropolis too after his death in 1331, though Ibn Khaldun wrote that he was buried in Fez. Construction of the main gate was finished by Abu al-Hasan, as evidenced by an inscription on it which dates its completion to July 1339 (Dhu al-Qadah 739 AH) and refers to the complex as a "ribat". During Abu al-Hasan's lifetime one of his wives, Shams al-Ḍuḥa (the mother of Abu Inan), was buried here in 1349. One of his sons, Abu Malik, may have also been buried in the necropolis in 1339. After his death in exile in 1351, Abu al-Hasan's body was buried in a mausoleum here as well, near his wife. This mausoleum may have been finished by his son and successor, Abu Inan (r. 1348–1358). Abu Inan may have also been responsible for building or completing the madrasa (Islamic college) and the prominent minaret that adjoin the mosque and mausoleums. He set up a charitable endowment (waqf) to fund the operations of the religious complex. Remains at the site today also show that the necropolis was accompanied by a residential quarter to the north, complete with a water supply system. A preserved hammam (bathhouse) from this period also stands near the far eastern corner of the walled enclosure.

Abu al-Hasan was the last sultan to be buried here. Abu Inan is believed to have been buried at the Great Mosque of Fes el-Jdid and other Marinid sultans after him were mostly buried at the Marinid Tombs in Fez or other sites. Other Marinid family members, such as Abu Inan's sister and other princes, were still occasionally buried at Chellah. Between 1360 and 1363 Ibn al-Khatib, the vizier of the Nasrid sultan Muhammad V, visited the site during his master's exile from Granada and mentioned it in his writings. He described the luxurious decoration of the tombs and noted that a large fragment of a kiswah (the cloth that covers the Ka'ba in Mecca) was draped over the tomb of Abu al-Hasan.

After the Marinid period the necropolis declined. It was pillaged for the first time by Ahmad al-Liḥyani, a pretender to the Marinid throne based in Meknes between 1417 and 1437. Although he and other pretenders were eventually suppressed by Abu Zakariya Yahya, the regent and de facto Wattasid ruler between 1420 and 1448, the Wattasids chose not to try and restore the necropolis. Many of the remaining structures in Chellah were damaged by the 1755 Lisbon earthquake and fell into ruins. The 'Alawi sultans stationed soldiers here afterwards to prevent further looting, but in the late 18th century an Arab tribe, the Ṣabbaḥ, took possession of the enclosure until in 1790 sultan Moulay Yazid charged the governor of Salé, Abu Ya'za al-Qasṭali, with removing them. During this episode the necropolis was again looted.

Despite this decline, the site acquired local religious importance over time. At some point, Sufis began to inhabit the site and the madrasa was reused as a zawiya (Sufi religious and educational center). The zawiya also became the object of a local pilgrimage, with locals believing that a visit here could be a substitute for the Hajj pilgrimage to Mecca for those who couldn't afford that long journey. As part of their visit, pilgrims performed a circumambulation (tawaf) of the madrasa's mihrab. Popular legends also grew around the tombs. The tomb of Shams al-Ḍuḥa came to be popularly known as the tomb of a girl named Lalla Chella, to which the site's name was popularly attributed. Some local beliefs, especially among women, associated beneficial maraboutic powers to some of the animals, like the eels and turtles, that lived in the pools here. For example, it was believed that feeding the eels could aid fertility and childbirth. Legends about buried treasures also led to illegal excavations at times and pushed authorities in the 20th century to move some of the most important objects in the necropolis to museums in Rabat.

The remains of the ancient Roman city were first identified in the late 19th century by French geographer Charles Tissot. The first investigation and study of the Islamic-era remains were carried out by Henri Basset and Évariste Lévi-Provençal in 1922. The first excavations of the Roman city were carried out in 1929–30 under the supervision of Jules Borély, head of the Service des Beaux-Arts, an agency of the French Protectorate in Morocco at that time. This initial work cleared away vegetation from the ruined mosque and unearthed a large portion of the "monumental" Roman quarter visible today. Excavations did not take place again until 1958, after Moroccan independence, when the head of the Service des Antiquités du Maroc, Maurice Euzennat, appointed Jean Boube to begin a new campaign of excavations. Excavations continued on and off until 1996, unearthing the rest of the structures now visible.

Today, the site of Chellah has been converted to a garden and tourist attraction. It is part of the metropolitan area of Rabat. The site, as part of historic Rabat, was listed by UNESCO as a World Heritage Site in 2012. It's also notable for hosting a large colony of storks, who nest in the trees as well as on the minaret of the ruined zawiya.

On 3 November 2023, a team of Moroccan archaeologists and researchers discovered the first port district of the Roman era in Morocco, dating from the first to the second century AD, along with the first life-sized headless statue of a female goddess found in Morocco since 1960.

The excavated portion of the Roman city covers about 1.2 hectares and corresponds to the "monumental" district around the forum, where the most important public buildings stood. The city was built on a sloped site and consequently its buildings were constructed upon a series of artificial terraces, with at least three terraces visible today. Streets were laid out in a regular grid and the two most important streets were the decumanus maximus and the cardo maximus.

At the eastern end of the excavated area is the forum. It is flanked on its north side by a structure standing on higher ground which has been identified as a "temple" with five cellae. On the south side of the plaza, on a lower level, is a long building with nine rooms, possibly tabernae (shops), that open onto another street. The dating of the temple and the adjoining forum has been debated. Jean Boube dated the temple to the mid-first century BC, which would make it a Mauretanian structure (before the region was annexed as a Roman province). Statues of the Mauretanian client kings Juba II and Ptolemy have been found here, leading Boube to suggest the temple was originally dedicated to them. Other archeologists have argued that it belongs instead to the Roman period (after annexation). More recent studies have again suggested a pre-Roman dating, based on the construction techniques present.