propping

Compelled, as they were, to await a night sufficiently dark to favor their flight, they were obliged to defer their final attempt till that auspicious moment should arrive; their greatest dread now was lest the stone through which the sentry was doomed to fall should give way before its right time, and this they had in some measure provided against by propping it up with a small beam which they had discovered in the walls through which they had worked their way.