At last, in December, they were free to take in hand the extraordinary scheme they had matured. This was, starting from a cellar of Percy's house,[142] to dig thence an underground mine to the foundations of the Parliament House, and through them; and then to construct within, beneath the Peers' Chamber itself, a "concavity" large enough to contain the amount of powder requisite for their purpose. On December 11th, 1604, they commenced operations,[143] and in a fortnight, that is by Christmas, they had tunnelled from their starting-point to the wall they had to breach; and that this first operation was of no small magnitude, especially for men who had never before handled pick or shovel,[144] is shown by the fact that what they contrived to do in so short a time was quoted as evidence of the extraordinary zeal they displayed in their nefarious enterprise.[145] Having rested a little, for the Christmas holidays, they began upon the wall, which presented an unexpected obstacle. They found that it was not only "very hard to beat through," but, moreover, nine feet thick, though since, as we shall see, they never penetrated to the other side, it is not clear how they were able to measure it.[146] Up to this point but five persons had engaged in the work, Catesby, Percy, Thomas Winter, John Wright, and Faukes. In consequence however of the difficulties now experienced, Keyes was called in to their aid. He had already been initiated in the Plot, and appointed to take charge of the powder, which was being accumulated and stored in a house hired for the purpose across the Thames, at Lambeth. It was therefore necessary to bring over the powder with him, which amounted at this time to twenty barrels, and was placed either in Percy's lodging itself, or in an outhouse belonging to it. About the same time Christopher Wright was also initiated and took his share of the labour.[147] The gang thus composed laboured upon the wall from the beginning of January, 1604-5, to the middle of March,[148] by which time they had succeeded in getting only half way through. While the others worked, Faukes stood on sentry to warn them of any danger.