The EGR system routes a number of the exhaust gases (6 ? 10%) over the EGR valve, in for the Intake System, and finally inside combustion chamber. The exhaust gases are inert i.e. they cannot burn within the combustion chamber; also, the exhaust gases take up many of the space which will rather be taken from the intake air. This reduces the level of intake air available for the combustion process during each Power Stroke; which experts claim decreases the peak combustion temperatures. This leads to lower NOx emissions. The Romans built several roads across Villamartin and also over time numerous artefacts happen to be discovered. Visigoth remains are also found. More recent finds happen to be from Arabic and Christian people. From the 8th century A.D. the complete region fell under Muslim control. The Matrera fields formed area of the Cora territory of Ronda. The closeness of Arcos, which belonged on the Cora de Medina, drove Omar Ben Hafsun, at the end of the 9th Century, to develop the fortress of Matrera, to defend Iptuci, one of the most advanced city within the Cora of Ronda.