The Trevi fountain is the most famous and beautiful fountain in all the world, this impressive monument dominates the small Trevi square located in the Quirinale district. The Trevi is at the ending part of the agua virgo that is an aqueduct that brings water all the way from the salone springs and supplies the fountains in the historic center of Rome with water. The fountain as it is know was constructed in 1732, Pope Clement XII commissioned Nicola Salvi to create a large fountain in the small square. A previous undertaking to build the fountain after a design by Bernini was halted a century earlier after death of Pope Urban VIII. Nicola Salvi based his theatrical masterpiece on this design. The construction was finally completed in 1762.
The central figure of the fountain is Neptune, god of the sea. He is riding a chariot in the shape of a shell, pulled by two sea horses, each sea horses is guided by a Triton. One of the horse is calm and obedient, the other one restive. They symbolize the fluctuating moods of the sea.
The water at the bottom of the fountain represents the sea. Legend has you will return to Rome if you throw a coin into the water, you should toss it over your shoulder with your back to the fountain. To be honest i haven't done it (about the coin) but I have spend three hours just looking at the Trevi fountain.