The only European grapes that are natively resistant to phylloxera are the Assyrtiko grape which grows on the volcanic island of Santorini, Greece, although it is not clear whether the resistance is due to the rootstock itself or the volcanic ash on which it grows; and the Juan Garcia grape variety, autochthonous to the medieval village of Fermoselle in Spain. The Juan Garcia variety remained—untouched by phylloxera—sheltered on the vineyards planted on the man-made land terraces along the mountainous skirts on the gigantic and steep Duero Arribes / Douro River Canyon, where the microclimatic conditions discourage the growth of phylloxera.