Notice the lion, Mulberry tree (with the red color beneath it) the dying man and woman stabbing herself. Together they tell us a tragic story from the ancient world. The painting is to be found in the so called House of Loreius Tiburtinus / House of D. Octavius Quartio. Other pictures from the same house may be found here and here.
Mythological motives are, as may be excepted, common. This painting depicts the story of Pyramus and Thisbe, a true Romeo and Juliet story. I will write a short summary, but you can read the full version as Ovid wrote it here.
Pyramus and Thisbe were living in two neighboring houses in Babylonia. I happened to be that they were madly in love and wished to be married, but family rivalry made that impossible and they could only speak to each other through a crack in the wall between the houses. One day they decided to go out and see each other, they were to meet up under the Mulberry tree at the tomb of Ninus. Thisbe was the first to arrive and she found a lion there, all bloody. Terrified, she ran away but dropped her veil. The lion took a bite of it and then left. Now Pyramus figured, when he arrived, that Thisbe had been killed. To sad to go on, he struck himself with his sword.
However, Thisbe returned to see her lover, she could not stay away from him, but found him dying under the Mulberry tree. She then cried out that she would also kill herself and now only wished two things; that the white mulberries would become forever red, as a reminder of the their death, and that she would be buried together with her love. She plunged the sword into herself and the mulberries were stained with her blood.
The gods granted her the first of the two wishes, her parents the second.