http://www.idbsu.edu/courses/hy101/peloponn/12.htmThe Peloponnesian War - Page 12 of 17
Nicias presented situation as hopeless, expecting that the Athenian
assembly, when it heard how poorly the expedition was proceeding, would
order him to come home. Instead, Athens sent him 15,000 more men, under
Demosthenes, creating thereby the largest army ever assembled in Greece.
Demosthenes was a dynamic general and tried an immediate offensive. But Syracuse was well defended and the attack failed. This attack was probably their best hope. When it failed, all the commanders began thinking of ways to withdraw the army safely.