There were frequent contacts between the Mozarabs in Al-Andalus and their co-religionists both in the Kingdom of Asturias and in the Marca Hispanica, the territory under Frankish influence to the northeast. The level of literary culture among the northern Christians was inferior to that of their Mozarab brethren in the historic cities to the south, due to the prosperity of Al-Andalus. For that reason, Christian refugees from Al-Andalus were always welcomed in the north, where their descendants came to form an influential element. Though impossible to quantify, the immigration of Mozarabs from the south was probably a significant factor in the growth in the Christian principalities and kingdoms of northern Iberia.