The Eastern Portico of the Apandana Palace is divided into three parts:
The northern staircase with representations of Achaemenid dignitaries,
The Staircase Centrepiece from which the pictures in this gallery are taken, and
The famous Southern Staircase showing representatives of all the subject nations.

The central bas relief shows the Zoroastrian Now Ruz symbol of a bull (Taurus, the spring equinox) being overcome by a Lion (Leo, the summer solstice), the bull's sacrifice leading to renewal.
(Note that the Taurus star sign was overhead at the time of the Spring Equinox 4000 years ago due to the precession of the earth.)

Originally all of the bas reliefs together with most of Persepolis itself were brightly coloured.
Where I have deemed appropriate I have enhanced the photographs in order to portray the bas reliefs at their best.