From Stamps of the World
Hay-on-Wye (Welsh: Y Gelli Gandryll), often abbreviated to just "Hay", is a small market town and community in Powys, Wales (in the former county and district of Brecknockshire), adjacent to the English border. Often described as "the town of books", it is the National Book Town of Wales.The settlement's name is first referred to between 1135 and 1147 as "Haya", later, in 1299 the name of "La Haye" is used. By the 16th century it is simply called "Hay" and the use of the river as a suffix is a later addition. In 1215, a Welsh name, "Gelli" was recorded, and "Gelli gandrell" in 1614, the two names may have been used concurrently as in 1625. The English name, "Hay", is derived from Old English "haeg", possibly meaning a "fenced area" and a noun used in late Saxon and Norman times for an enclosure in a forest. The Welsh "Gelli" has a range of meanings including wooded areas of various extents.
Hay was allocated the numeral 347