The historic town centre is well preserved and is protected by law as an urban monument zone.

According to the Wenceslaus Hajek's chronicle records, Slaný was founded at the site of a salt spring below the hill of Slánská hora.

The highest point and a dominant feature of the town's panorama is the hill Slánská hora at 330 m (1,080 ft) above sea level.

It was this large presence of the church, and the unconsolidated state of landed property that went with it, that allowed King Wenceslaus II of Bohemia to charter Slaný as a town and give his royal assent to its Magdeburg rights only sometime in the decade after 1295.

[3] In 1348, an earthquake damaged the now-fortified town; in 1371, a large fire broke out, and the church had to be rebuilt.

Not only did the Benedictine monks have to leave — this town by the hill was also one of Hussite holy cities, and their preachers expected it to survive the anticipated end of the world.

Later, King George of Poděbrady gave Slaný many privileges, after the town had supported his election to the throne.

The town also participated in the Bohemian Revolt that opened the Thirty Years' War, housing the family of King Frederick V. After the Battle of White Mountain, that meant a defeat for the cause, the town suffered as a result of the ravages of war.

Afterwards, the new Catholic possessors of Slaný, the Martinic family, erected a Baroque church and edifice that, together with a new monastery, adorn the town to this day.

Slaný is the terminus and starting point of the railway line from/to Kralupy nad Vltavou.