 From the sixth century , Scotland experienced a process of Christianisation , traditionally seen as carried out by Irish @-@ Scots missionaries , including St Ninian , St Kentigern and St Columba and to a lesser extent those from Rome and England . However , Gilbert Markus highlights the fact that most of these figures were not church @-@ founders , but were usually were active in areas where Christianity had already become established , probably through gradual diffusion that is almost invisible in the historical record . This would have included trade , conquest and intermarriage . 
