American mustangs are feral horses and protected by law since 1971. Originally, they were descendants of Spanish horses, brought over by the conquistadors. More recently, over the last 100 or 150 years, they were increasingly "contaminated" by horses of all kinds of origins. However, in isolated areas of the West, herds of predominantly Spanish mustangs survived. Columbus's diary contains records which suggest that horses of the Sorraia kind were shipped to the New World at least once. This could account for the fact that the relatedness of some mustangs with the Sorraia was scientifically proved, and that mustangs of Sorraia type can still be found.