Nanoindentations resulting from STM tungsten tip contacts with the 5×20 reconstructed surface of a Au(001) crystal around the indentation point have been studied by Scanning Tunnel Microscopy (STM). A novel defect structure is recognised: a row of hillocks extending along more than a hundred nm along the <110> directions stemming from the indentation point. These hillocks have about 7 nm of side and 0.06 nm of height. With the help of simulation models we identify individual hillocks as dislocation configurations consisting of two stacking fault ribbons encompassed by Shockley partials having a stair-rod dislocation as a ridge. It is proposed that hillocks are generated by plastic flow, from an initially nucleated V-shaped dislocation loop intersecting the surface.