In WA Cummins, The Age of the Picts, Stroud:1996, on page 75, there is a symbol of a double disc and a Z Rod (see below). According to Cummins this image was a symbol that was used by the famous king of the Picts, Drust son of Erp – extent in the 5th century AD. Gildas appear to refer to his conquest of southern Scotland (which included Galloway and the Christian community at Whithorn) (see also NJ Higham, The English Conqest: Gildas and Britain in the 5th century, Manchester University Press: 1994) – which of course would have also included the territory of the Votadini. Drust son of Erp is said to have ruled for a 100 years and fought 100 battles – a figure of speech but indicating an exceptionally long reign with the kind of conflict to match the wide area that accrued around him as high king of the Pictish alliance. St Ninian’s converts in Galloway and elsewhere would have found themselves in a kingdom controlled by a non-Christian, and this is the situation reflected in St Patrick’s letter to Coroticus. He controlled a large area of Scotland, including the region immediately north of Hadrian’s Wall (a region contested in the next couple of centuries by the expansion of the Anglian kingdom of Northumbria) but his main seat of power was in all likeihood in Perthshire and the eastern side of Scotland (uniting various tribes). The double disc and Z Rod symbol is found in many places – including Traprain Law, the hill fort associated with the Votadini, and according to Cummins where ever it is found, on artefacts or on stones and monuments it was the mark of Drust, and his conquests.
However, Drust, the name of a king suggests he was also the name of a god, and indeed this is so. In Latin it is written Drustanus and became Dystan in Welsh, and Tristan or Tristram of Arthurian Romance. The legend of Tristram and Isolde is a tale that is well known but as a member of the Round Table Tristan was associated with the killing of a giant. Did he use the Z Rod, which looks something like a lightning bolt, or discharge.