They naturally thought of Cleopatra as a manipulative seductress, because she had earlier seduced Julius Ceasar who was thirty years her senior, and her sexual exploits were well known. The Romans were led by Octavius, Octavia's brother who charged in to conquer Egypt and overcome Mark Anthony.
Overwhelmed by the Roman forces, Mark Antony chose death by suicide over being captured. After his death and facing the prospect of Roman invasion, Cleopatra chose death as well. As someone who has experimented with poisons on prisoners on different occasions, she knew that the venom of the asp was the least painful and a relatively quicker way of dying. Most privileged or political prisoners were executed in this way by the Egyptians and by the Greeks before them. At this point of time, all serpents were known as asps, and the snake Cleopatra used for her suicide was probably the Egyptian cobra Naja Haje.
The cobra was revered by the ancient Egyptians possibly because they lived in close proximity with it, because the rodents commonly associated with humans were their natural prey. Egyptians lost a lot of their own to this snake's potent venom. It was placed on the crown of the Egyptian pharaohs, and was in fact the Royal symbol. It represented the "fiery eye of Re", in which there are two uraei which are placed on either side of a winged solar disk.