As some Jews were engaged in trade, which carried them further afield, they were perhaps better informed about potentially hostile neighbors.
Jews were included in such militias despite anti-Semitic feelings as seen in the discussion by Karo and Sirkes mentioned earlier. Although the number of Jews in any community was small, every person counted and every able bodied man was needed. Their participation did not lead to better relations in peaceful times. We should note that the Jewish community were usually too small to undertake successful self-defense during riots by the local population. Jews fighting to defend a city were taken for granted by the rabbinic authorities without any halakhic discussion. Presumably Jews fought on shabbat when needed along with everyone else. Such defensive engagements in contrast to the adventures of ambitious monarchs were accepted without discussion. We know that in Spain Jews joined local militia in defense of their towns and occasionally also served in royal armies. *’ Alfonso VI in 1086 even proposed that the battle of Sacralias-Zallaka be postponed from Friday to Monday so that the holy days of Muslims , Christians , and Jews would not interfere.”
A few Jews were involved in battle; among them was Samuel Ha-Nagid (993-1056) who is said to have written some of his beautiful poetry on the battlefield, but we do not know whether he actually fought.”* During the period of the Crusades , Jews defended themselves by donning“their armor and girding on their weapons, and at their head was Rabbi Kalonymous ben Meshullam.”” At about the same time the Messianic pretender, David Alroy, appealed to the Jews of Persia for assistance in an armed uprising which was to conquer Jerusalem .”
During the Crusades some Jews went further and organized units to defend their community against the Crusaders. As those armies marched through the Rhineland , they attacked the Jewish communities as well as the towns in which they lived. The Christian neighbors often also fought to defend them, but usually in vain. When the besiegers left, the military service ceased, for those who survived.”