Falaj (pl. aflaj), meaning 'water channel', is the Arabic term used in the Arabian peninsula for the system known in Persian as qanat and karîz. This is an ingenious method of irrigation which takes advantage of groundwater trapped in sub-surface aquifers and channels it from the piedmont or foothill zones where it is most easily reached, to date-gardens and cultivated oases in lower lying elevations. Falaj systems are begun in the piedmont by excavating a vertical shaft down to the water table. At the point where water is reached a horizontal tunnel or gallery is then excavated away from the piedmont towards the gardens and villages requiring water. At regular intervals additional vertical shafts are dug down to the gallery, providing access for the repairs and gallery cleaning which will have to occur through time so long as the falaj is in use. Thus, from the air, a falaj system appears as a series of dots leading from the mountains to an ultimate point at which the water empties out of its sub-surface channel into a holding tank or series of smaller, above-ground channels running through a garden. Such falaj systems are known to run for many kilometres and to remain in use for centuries. In the Emirates, well-preserved examples can be seen around Al Ain (where an ancient system dating to the Iron Age has been excavated), al-Madam, Falaj al-Mualla and elsewhere.