A chronicler reports that Frederick received a demand of submission from Batu Khan at some time, which he ignored. He apparently kept up to date on the Mongols' activities, as a letter from Frederick II dated June 1241 comments that the Mongols were now using looted Hungarian armor. A letter written by Emperor Frederick II, found in the Regesta Imperii, dated to June 20th 1241 and intended for all his vassals in Swabia, Austria, and Bohemia, included a number of specific military instructions. His forces were to avoid engaging the Mongols in field battles, hoard all food stocks in every fortress and stronghold, and arm all possible levies as well as the general populace. Thomas of Split comments that there was a frenzy of fortifying castles and cities throughout the Holy Roman Empire, including Italy. Either following the Emperor's instructions or on their own initiative, Frederick II, Duke of Austria paid to have his border castles strengthened at his own expense while King Wenceslaus I of Bohemia had every castle strengthened and provisioned, as well as providing soldiers and armaments to monasteries in order to turn them into refuges for the civilian population. Mongol probing attacks did materialize on the HRE's border states: a Mongol attack on Olomouc failed (the leader being captured in a sortie), a force was repulsed in a skirmish near Kłodzko, 300-700 Mongol troops were killed in a battle near Vienna to 100 Austrian losses (according to the Duke of Austria), and a Mongol raiding party was destroyed by Austrian knights in the district of Theben after being backed to the border of the River March. However a full-scale invasion never occurred, as the Mongols spent the next year pillaging Hungary before withdrawing. After the Mongols withdrew from Hungary back to Russia, Frederick turned his attention back towards Italian matters.
They would have slammed into an unbreakable German wall of fortresses and crossbows.