Criminal conspiracies were taken very seriously by the Yankees of Massachusetts. Slavery was well-established in the state, and after 1750 many residents began to profit from the Triangle Trade. Slaves and molasses were imported from the British Sugar Colonies in the Caribbean, and rum was distilled here using the molasses, and sold to Europe and elsewhere.
In 1755, several slaves had conspired to kill their owner. It's lost to history whether the owner had sadistically abused his slaves and prompted a rebellion, or if merely a band of murderers had decided to kill their benevolent head of household. In any case, Mark and Phillis were executed on September 18, 1755 for murdering their owner.
An intriguing fact about the executions is that Phillis was burned at the stake as punishment. There is only one other case in Massachusetts history where a person was burned at the stake, that of Maria, also an African servant, who attempted to murder her owner by setting his house on fire. Also, Mark was hanged until dead, and his body was then gibbeted, or publicly displayed in chains, a fate usually reserved for pirates. His body remained at Charlestown for an astounding twenty years, and became a well-known landmark.
The following is an account of the conspiracy by the Massachusetts Historical Society (1883):
"Captain John Codman, a thrifty saddler, sea-captain, and merchant, of Charlestown, was the owner of several slaves whom he employed either as mechanics, common laborers, or house servants. Three of the most trusted of these, Mark, Phillis, and Phebe, — particularly Mark, — found the rigid discipline of their master unendurable, and, after setting fire to his workshop some six years before, hoping by the destruction of this building to so embarrass him that he would be obliged to sell them, they, in the year 1755, conspired to gain their end by poisoning him to death.
In this confederacy some five or six [blacks] belonging to other owners were more or less directly implicated. Mark, the leader, was able to read, and signed his examination, hereafter referred to, in a bold, legible hand. He professed to have read the Bible through, in order to find if, in any way, his master could be killed without inducing guilt, and had come to the conclusion that according to Scripture no sin would be committed if the act could be accomplished without bloodshed.
It seems, moreover, to have been commonly believed by the [blacks] that a Mr. Salmon had been poisoned to death by one of his slaves, without discovery of the crime. So, application was made by Mark, first to Kerr, the servant of Dr. John Gibbons, and then to Robin, the servant of Dr. Wm. Clarke, at the North End of Boston, for poison from their masters' apothecary stores, which was to be administered by the two women. Essex, the servant of Thomas Powers, had also furnished Mark with a quantity of 'black lead' for the same purpose. This was, unquestionably, not the harmless plumbago to which that name is now usually given, but galena, or plumbum nigrum, a native sulphuret of lead, probably used for a glaze by the potters of Charlestown.
Kerr declined to have any hand in the business; but Robin twice obtained and delivered to Mark a quantity of arsenic, of which the women, Phebe and Phillis, made a solution which they kept secreted in a vial, and from time to time mixed with the water-gruel and sago which they sometimes gave directly to their victim to eat, and at other times prepared to be innocently administered to him by one of his daughters. They also mixed with his food some of the 'black lead,' which Phillis seems to have thought was the efficient poison, though it appeared from the testimony that he was killed by the arsenic.
The crime was promptly traced home to the conspirators; and on the second day of July, the day after Captain Codman's death, a coroner's jury found that he died from poison feloniously procured and administered by Mark. Ten days later, Quaco, — the nominal husband of Phebe, and one of the [blacks] implicated, — who was the servant of Mr. James Dalton, of Boston, was examined before William Stoddard, a justice of the peace, and on the same day Robin was arrested and committed to jail. The examination of Quaco was followed by the examination of Mark, and of Phillis, later in the month. These last were taken before the Attorney-General and Mr. Thaddeus Mason."
Mark and Phillis were eventually found guilty of murder, and were both sentenced to death for their crime. The September 25, 1755 Boston News-Letter describes their execution:
"Thursday last were executed at Cambridge, pursuant to their sentences, Mark and Phillis, two Negro Servants belonging to the late Captain John Codman of Charlestown, for poysoning their said Master: They were both drawn from the Prison to the Place of Execution, attended by the greatest Number of Spectators ever known on such an Occasion; where the former was hanged by the Neck until dead, after which the body was Gibbeted; and the latter was burned to Death."
The September 22, 1755 Boston Evening Post also describes their execution:
"Thursday last, in the Afternoon, Mark, a Negro Man. and Phillis, a Negro Woman, both Servants to the late Capt. John Codman, of Charlestown, were executed at Cambridge, for poisoning their said Master, as mentioned in this Paper some Weeks ago. The Fellow was hanged, and the Woman burned at a Stake about Ten Yards distant from the Gallows. They both confessed themselves guilty of the Crime for which they suffered, acknowledged the Justice of their Sentence, and died very penitent. After Execution, the Body of Mark was brought down to Charlestown Common, and hanged in Chains, on a Gibbet erected there for that Purpose."
A strange fact about the case is that Mark's body was gibbeted, a punishment usually doled out for pirates (at Nix's Mate in Boston Harbor). Gibbeting, or hanging a dead body in chains, was a symbolic deterrent to potential criminals, and was also considered comforting to the victim's family at the time. Mark's body was chained to a pole after the execution, and remained there for twenty years. Paul Revere had stated in a letter about his famous Midnight Ride of 1775: "After I had passed Charlestown Neck, and got nearly opposite where Mark was hung in chains, I saw two men on horseback under a tree." It seems quite gruesome that Mark's body had become a landmark like the Boston Stone or Liberty Stump.
It is unclear if the other conspirators were executed, but it is likely they were sent to the sugar colonies in the Caribbean to work the fields, a standard form of punishment at the time.