Nicias, again, the Athenian general, could have saved the army before <a class="linkToPlace" target="_blank" href="/place?placename=Syracuse&groupId=994&placeId=1753">Syracuse</a>, and had fixed on the proper hour of the night to withdraw into a position of safety unobserved by the enemy; but on an eclipse of the moon taking place he was struck with terror as if it foreboded some calamity, and deferred his departure.
The consequence of this was that when he abandoned his camp on the following night, the enemy had divined his intention, and both the army and the generals were made prisoners by the Syracusans.
Yet had he only inquired from men acquainted with astronomy so far from throwing away his opportunity owing to such an occurrence, he could have utilized the ignorance of the enemy.
For nothing contributes more to the success of well-informed men than the lack of instruction in their neighbour sand
So far as the points I have mentioned are concerned it is to astronomy that we should address our inquiries, but the method of discovering right length for ladders is as follows.
If any of our partisans can give us the height of the wall the required length of the ladders is evident. For if the height of the wall be, let us say, ten of a given measure, the length of the ladders must be a good twelve.
The distance from the wall at which the ladder is planted must, in order to suit the convenience of those mounting, be half the length of the ladder, for if they are placed farther off they are apt to break when crowded and if set up nearer to the perpendicular are very insecure for the scalers. If how it is impossible to measure the wall or approach it, the height of any object which stand perpendicular on a plane surface can be taken from a distance, the method of determining it being practicable and easy for anyone who chooses to study mathematics.
Walbank Commentary