Mechanical "dragons" were siege engines built by the Alchemists' Guild under orders of King Aegon IV Targaryen to replace the extinct dragons of House Targaryen.
Like many other Targaryen kings, Aegon was obsessed with regaining dragons for his house. Instead of trying to resurrect the dead dragons of his ancestors, Aegon instead turned to the pyromancers and commanded them to "build me dragons". The Guild built seven wood and iron monstruous engines, fitted with pumps that shot jets of wildfire. Upon their completion, Aegon ordered these devices dragged to the Boneway to initiate the invasion of Dorne in 174 AC. The king's plan lacked any tactical sense, as the Boneway was too steep for the lumbering constructs. The man-made dragons did not even reach that far, due to instability of wildfire and the difficulty of moving the massive siege engines. All seven were consumed by fire in the kingswood; hundreds of men operating them burned alive inside them and a quarter of the kingswood went up in flames. Aegon, after this humiliation, never spoke of Dorne again.
- ↑ 1.0 1.1 The World of Ice & Fire, The Targaryen Kings: Aegon IV.