A giant swastika, trampled into a cornfield is pictured at a farm in the village Niklasreuth near Assling, about 30 km near the southern Bavarian town of Rosenheim, August 24, 2010. REUTERS/Michael Dalder

BERLIN - German prosecutors said on Tuesday they had launched an investigation into a giant swastika figure trampled into a maize field and visible only from the air.

Police in Assling, Bavaria, said the swastika, like all Nazi insignia illegal under German law, was spotted on Sunday by a pilot flying from a nearby airfield. There were no leads to the perpetrators of the offending symbol, which is about 20 metres by 20 metres in size.

The field is due to be harvested in three weeks. It was not clear whether the farmer would be obliged to trample down more of the crop to obscure the swastika — something German media said would be a costly affair.