Durdle Door is a natural limestone arch on the Jurassic Coast near Lulworth in Dorset. The 120-metre (390 ft) isthmus that joins the limestone to the chalk is made of a 50-metre (160 ft) band of Portland limestone. In 1811 the first Ordnance Survey map of the area named it as "Dirdale Door". Durdle is derived from the Old English thirl, meaning to pierce, bore or drill, which in turn derives from thyrel, meaning hole. The Door part of the name probably maintains its modern meaning, referring to the arched shape of the rock; in the late 19th century there is reference to it being called the "Barn-door", and it is described as being "sufficiently high for a good-sized sailing boat to pass through it." England.?