A striking entity of Pincio Gardens is the obelisk. Emperor Hadrian decided to put the Egyptian-style obelisk in the park during the second century AD. He wanted this obelisk in memory of his favorite slave- Antinous. According to some reports, Antinous died saving the emperor’s life. The obelisk was put in the gardens in 1822 by Pope Pius VII.
*Added information taken from DK Eyewitness Guide to Rome and http://www.aviewoncities.com/rome/pinciogardens.htm