Sennaya Square or Sennaya Ploshchad (Russian: Сeннáя Плóщадь, literally: Hay Square), known as Peace Square between 1963 and 1991, is a large city square in Central Saint Petersburg, located at the crossing of Garden Street, Moskovsky Prospekt, and Grivtsova Lane.
The square was established in 1737 as a market where hay, firewood and cattle were sold. It was built under the extension of the Garden Street, and grew quickly, becoming the cheapest and the most active market in Saint Petersburg. The Hay Market was a place where merchants and farmers could trade. It was there that malefactors were flogged before a large concourse of people.
In 1753, the Church of the Assumption of the Mother of God was built in a sumptuous Baroque style. In the middle of the square is a former guardhouse (1818–20). The square was a venue for the cholera riots of 1831. The surrounding district was known for its infamous slums, which provide the setting for Dostoevsky's novel Crime and Punishment.
In 1961 the church was pulled down to make place for a new metro station. Its place is now marked by a chapel. The 17,5 meter high "Peace Column", a gift of France to the tercentenary of St. Petersburg, was dismantled during the heatwave of 2010. The column featured the word "peace" written in 49 languages.
The square is served by three metro stations; Sennaya Ploshchad, Sadovaya and Spasskaya. It is also a bus and marshrutka station. It used to have regular tram transportation until 2010, a fragment of the tram rails having been preserved as a historical mark.