The Hard X-ray Imaging Spectrometer aboard the SMM detected gigantic arches in the corona which are formed or, if preexisting, become excited after major two-ribbon flares. They are seen in 3.5-8 keV X-rays and extend along the Hjl = 0 line to altitudes between l0 s and 2 x 105 km. These arches are stationary and form the base of a stationary type I radio noise storm initiated by the flare. They are visible in X-rays for ten hours or more and may be revived, in temperature, density, and brightness, if another two-ribbon flare appears below them. We suggest that they are built-up through reconnection process during the flare from the upper reconnected loops in the Kopp and Pneuman model. These loops become interconnected along the HII = 0 line in consequence of great shear of the reconnecting loops. Obviously, the coronal transient associated with such flares must be either accomplished prior to the formation &the arch, or it must be formed through a process different from the Anzer-Kopp-Pneuman mechanism.
Striking brightness variations occur quasi-periodically in the corona below and above the arch a few hours after the flare. These variations are seen at about the same time in soft X-rays, hard X-rays, and on centimeter microwaves in the low corona, as well as at metric waves in the type I noise-storm region. In spite of their flare-like intensity, however, the variations have little response in the transition layer (O v line) and no response at all in the chromosphere (He). We suggest that these semi-periodic brightenings are due to repetitive acceleration processes in plasmoids that encircle the arch perpendicular to the HII = 0 line from the low corona through the noise storm region, being completely detached from the lower atmospheric layers.