Almost due south from the town of Wrexham is Oswestry. It is the southern most anchor of Wat's dyke leading to the ancient hill fort called "Old Oswestry Hill Fort". Strictly speaking, according to James Dyer, "hillforts" were hilltops defended by walls of stone, banks of earth or fences of wood, usually accompanied by one or more external ditches. They are generally associated with the iron age folks, starting around 800 B.C.
Old Oswestry, Selattyn, is considered one of the most complex of this periods hillforts. The fortifications cover about 40 acres, and in parts, has as many as seven ramparts. The hill top contains roughly 16 acres, and is felt by Professor W.J. Varley (excavated site in 1939), at first to have contained a group of circular timber-built huts. Two ramparts were built at a later date, encircling the hill, which by this time contained circular stone huts. Over time, further changes took place extending the defenses, building one of the most complex series of deep hollows and ridges. [More will be said about this later.] This fortification certainly took advantage of a lofty, natural eminence, and is traditionally felt to be the ancient site of the town of Oswestry. Wat's Dyke connects here, and it certainly would have been occupied before this dyke was built. It is around this area that much of my JONES family had its roots. Perhaps, this "Hen Dinas" was the first location of my Celtic tribe.
The reference is : "Prehistoric England and Wales", by James Dyer, Penguin Books, 1981. Old Oswestry is discussed on pages 220-221. Hill forts are discussed on pages 33-34.