The Ruin (Stone) Bridge is located in one of the most beautiful places of the Upper Park of Oranienbaum — it spans the Karosta River and is situated in the Petrovsky Park area, which is often called the Russian Switzerland.

At the end of the 18th and beginning of the 19th century, the Upper Park fell into a neglected state. Many plants died, others grew wild from self-seeding. Shortly after the death of Alexander I, from 1827 the estate came under the ownership of his brothers Konstantin and Mikhail. From that time, under the guidance of gardener Joseph Bush Jr., work began on the arrangement of the estate.

Instead of the formal park created in the 18th century according to Antonio Rinaldi’s design, a landscape park with groves and clearings appeared. Instead of dams, cascades were built, and boulders appeared near their bases and along the riverbed. Across the Karosta, the three-arched Petrovsky Bridge and the small two-arched Ruin Bridge were thrown, corresponding to the romantic tastes of the 19th century.

The landscape opening from the wooden Ruin Bridge was so beautiful that it caused delight and sighs from the guests of the park in Oranienbaum. It is no surprise that the bridge was often called the Bridge of Sighs. The pylons and railings of the structure were wooden.

At the beginning of the 20th century, the bridge was rebuilt in stone and became known as the New Bridge. The name "Ruin Bridge" appeared in 1945, when the wooden railings were lost.

Source:

https://www.spb-guide.ru/ruinnyj-most-oranienbaum.htm