The present paper deals with the constructional treatments in Mosul in regard to the nature of site and the maintenance of buildings. This includes reducing the effect of environment, reinforcing foundations, pressure on ceilings as well as distributing pressure on walls all characteristics of civil engineering in Islamic ages. The ancient site of Mosul sloped gradually to the south and south-east which facilitated drainage of rainfall towards the Tigris river and kept underground waters off the foundations of buildings. Condensed groups of buildings increased their solidity while dome-shaped ceilings reduced the pressure on walls and foundations as the weight was distrilouted equally on them. At the same time, using columns in public buildings reduced the pressure of ceilings on the foundations and walls while the paired stairs the architects used in the Noori Mosque minaret reduced the pressure on its base and increased the tightening power of building materials round its middle axis. The lower part of the walls was covered from inside with marble belts to prevent wetness. The constructional treatments of buildings used local materials like limestone, gypsum, lime and bricks. Limestone helped increase the thickness of walls and reduced fracturesdue to its low expansion and contraction relative to changes in temperature, while gypsum is the best stone binding material. As for lime, it is the most suitable material for laying foundations.