It seems probable that these sweeping expeditions at length aroused the Arabians to the danger that threatened them all. At all events, in the early months of 627 it happened that a confederacy of Koreishite, Bedouin and Jewish tribes put an army numbering approximately ten thousand men in the field against Medina. The Prophet well knew that the memories of Uhud, still rankling in the minds of his compatriots, made it highly inexpedient to desert the city and meet the oncoming foe in the open field. Yet Medina must be defended at all costs--everyone, even the most feeble-kneed, was agreed upon that--and feverish counsels were held to devise a plan whereby the city might be made impregnable against assault. At this crucial juncture, a Persian ex-slave suggested that the city be entrenched in the same way as, in his travels, he had observed that the Mesopotamian cities were protected. Acting immediately upon his inspired advice, the Moslems filled in the gaps between their outer line of stone houses with a stone wall; and, at the southeastern quarter, which was entirely defenseless, a deep and wide ditch was dug. After six days of prodigious and incessant labor, the trench was completed. The Prophet threw himself heartily into the work, and, dirty and weary as he was, joined his stentorian voice in unison with the other toilers as they once again intoned the words: “O Lord! there is no happiness but that of Futurity. O Lord! have mercy on the Citizens and the Refugees!” The result was that, when Abu Sufyan came marching up at the head of his conglomerate force, all that he could do was to permit his troops to shoot some harmless showers of arrows, pitch his tents, sit down, and wait for the Moslems to come forth. Entrenchments as a military device were entirely unknown in Arabia; so the invaders logically concluded that Mohammed was not a good sport--as on other occasions, he had violated the Arabic code of chivalry by proving that he had brains. “Truly this ditch is the artifice of strangers,” they yelled, “a shift to which no Arab yet has ever stooped!” But the Moslems did not take the hint, and so next day the besiegers made a gallantly unsuccessful attempt to rush the barricade by sheer weight of numbers. Nevertheless, the assault accomplished one very irritating thing: for a whole day the devoutest of the Moslems had been prevented from saying their prayers. Gratifying amends for this forced neglect of Allah, however, were made when night fell; at that time an individual service was held for each omitted supplication, and Mohammed contributed a special comminatory request: “They have kept us from our daily prayers; God fill their bellies and their graves with fire!” Indeed, while the siege lasted, the Prophet spent most of the hours in protracted prayer, though he managed to find time enough to guard himself against the threatening activities of the Jews and other disaffected Medinese. Nor did his devices stop here.