Archaeologists have uncovered a series of "unique" Christian wall paintings at a dig in Sudan.

The excavation explored a complex of small rooms at Old Dongola, the one-time capital of the Nubian kingdom of Makuria and situated in present-day Northern State, Sudan.

The team, led by Dr Artur Obłuski from the Polish Centre of Mediterranean Archaeology, at the University of Warsaw, was exploring several houses dating from the Funj period (16th-19th centuries AD) when they stumbled across a hidden chamber beneath one of the floors. 

Inside the chamber, the interior walls were decorated with paintings showing the Virgin Mary, Christ, the Archangel Michael, and a Nubian king believed to be David, one of the last rulers of Christian Makuria before the kingdom's demise.

The archaeologists said that the scenes were "unique for Christian art". 

"However, this was not a typical representation of a Nubian ruler under the protection of saints or archangels," they said.

"The king bows to Christ, who is seated in the clouds, and kisses his hand. The ruler is supported by Archangel Michael, whose spread wings shield both the king and Christ himself.

"Such a scene finds no parallels in Nubian painting.

"The dynamism and intimacy of the representation contrasts with the hieratic nature of the figures shown on the side walls."

On the north wall of the chamber, the Virgin Mary was depicted "in a dignified pose", dressed in dark robes, and holding a cross and book in her hands. 

The researchers said that this figure did not reflect typical depictions of Mary in Nubian art. 

The figure of Christ was depicted on the opposite wall with a book in his left hand and holding his right hand in a gesture of blessing. 

A preliminary study of the Greek inscriptions found alongside the paintings reveals references to a king named David and a plea to God for protection of the city, believed to be Dongola.

"For reasons unknown, King David attacked Egypt, which retaliated by invading Nubia and, as a result, Dongola was sacked for the first time in its history. Maybe the painting was created as the Mamluk army was approaching the city or already laying siege to it?" they said. 

The complex of rooms was found next to another building "identified as the Great Church of Jesus, which was probably the cathedral of Dongola and the most important church of the kingdom of Makuria".

"Arab sources recounting King David's attack on Egypt and the capture of the port of Aidhab and Aswan, maintain that this act was instigated by the Great Church of Jesus. Did the Archbishop of Dongola, much like Pope Urban II, incite King David to launch a crusade?" they said. 

"Further excavations may provide answers to these and other questions about the enigmatic structure. However, the most important objective this season was to preserve the unique wall paintings."

The excavation at Old Dongola was financed by the European Research Council. Research continues at the site.