From http://en.wikipedia.org/wiki/Herma:

In 415 BC, on the night before the Athenian fleet was about to set sail for Syracuse during the Peloponnesian War, all of the Athenian hermai were vandalized. This was a horribly impious act and many people believed it threatened the success of the expedition. Though it was never proven, the Athenians at the time believed it was the work of saboteurs, either from Syracuse or anti-war doves from Athens itself. In fact, Alcibiades was accused of being the originator of the crime. He denied the accusations and offered to stand trial, but the Athenians did not want to disrupt the expedition any further. His opponents were eager to have Alcibiades' trial in his absence when he could not defend himself. Once he had left on the expedition, his political enemies had him charged and sentenced to death in absentia, both for the mutilation of the herms, and the supposedly related crime of profaning the Eleusinian Mysteries.

Thucydides, The History of the Peloponnesian War, Book 6:

In the midst of these preparations all the stone Hermae in the city of Athens, that is to say the customary square figures, so common in the doorways of private houses and temples, had in one night most of them their fares mutilated. No one knew who had done it, but large public rewards were offered to find the authors; and it was further voted that any one who knew of any other act of impiety having been committed should come and give information without fear of consequences, whether he were citizen, alien, or slave. The matter was taken up the more seriously, as it was thought to be ominous for the expedition, and part of a conspiracy to bring about a revolution and to upset the democracy.

Information was given accordingly by some resident aliens and body servants, not about the Hermae but about some previous mutilations of other images perpetrated by young men in a drunken frolic, and of mock celebrations of the mysteries, averred to take place in private houses. Alcibiades being implicated in this charge, it was taken hold of by those who could least endure him, because he stood in the way of their obtaining the undisturbed direction of the people, and who thought that if he were once removed the first place would be theirs. These accordingly magnified the matter and loudly proclaimed that the affair of the mysteries and the mutilation of the Hermae were part and parcel of a scheme to overthrow the democracy, and that nothing of all this had been done without Alcibiades; the proofs alleged being the general and undemocratic licence of his life and habits.

Alcibiades repelled on the spot the charges in question, and also before going on the expedition, the preparations for which were now complete, offered to stand his trial, that it might be seen whether he was guilty of the acts imputed to him; desiring to be punished if found guilty, but, if acquitted, to take the command. Meanwhile he protested against their receiving slanders against him in his absence, and begged them rather to put him to death at once if he were guilty, and pointed out the imprudence of sending him out at the head of so large an army, with so serious a charge still undecided. But his enemies feared that he would have the army for him if he were tried immediately, and that the people might relent in favour of the man whom they already caressed as the cause of the Argives and some of the Mantineans joining in the expedition, and did their utmost to get this proposition rejected, putting forward other orators who said that he ought at present to sail and not delay the departure of the army, and be tried on his return within a fixed number of days; their plan being to have him sent for and brought home for trial upon some graver charge, which they would the more easily get up in his absence. Accordingly it was decreed that he should sail. 

Plutarch, Life of Alcibiades, 18.2:

After the people had adopted this motion and all things were made ready for the departure of the fleet, there were some unpropitious signs and portents, especially in connection with the festival, namely, the Adonia. [3] This fell at that time, and little images like dead folk carried forth to burial were in many places exposed to view by the women, who mimicked burial rites, beat their breasts, and sang dirges. Moreover, the mutilation of the Hermae, most of which, in a single night, had their faces and forms [phalli] disfigured, confounded the hearts of many, even among those who usually set small store by such things. It was said, it is true, that Corinthians had done the deed, Syracuse being a colony of theirs, in the hope that such portents would check or stop the war. [4] The multitude, however, were not moved by this reasoning, nor by that of those who thought the affair no terrible sign at all, but rather one of the common effects of strong wine, when dissolute youth, in mere sport, are carried away into wanton acts. They looked on the occurrence with wrath and fear, thinking it the sign of a bold and dangerous conspiracy. They therefore scrutinized keenly every suspicious circumstance, the council and the assembly convening for this purpose many times within a few days.

Plato, Symposium:

When Socrates had done speaking, the company applauded, and Aristophanes was beginning to say something in answer to the allusion which Socrates had made to his own speech, when suddenly there was a great knocking at the door of the house, as of revellers, and the sound of a flute-girl was heard.  Agathon told the attendants to go and see who were the intruders. “If they are friends of ours,” he said, “invite them in, but if not, say that the drinking is over.”  A little while afterwards they heard the voice of Alcibiades resounding in the court ; he was in a great state of intoxication and kept roaring and shouting “Where is Agathon?  Lead me to Agathon,” and at length, supported by the flute-girl and some of his attendants, he found his way to them. “Hail, friends,” he said, appearing at the door crown, with a massive garland of ivy and violets, his head flowing with ribands. “Will you have a very drunken man as a companion of your revels?  Or shall I crown Agathon, which was my intention in coming, and go away?  For I was unable to come yesterday, and therefore I am here to-day, carrying on my head these ribands, that taking them from my own head, I may crown the head of this fairest and wisest of men, as I may be allowed to call him. Will you laugh at me because I am drunk?  Yet I know very well that I am speaking the truth, although you may laugh. But first tell me ; if I come in shall we have the understanding of which I spoke?  Will you drink with me or not?”