Marian columns are religious monuments built in honour of the Virgin Mary, often in thanksgiving for the ending of a plague or for some other help. The purpose of the Holy Trinity columns was usually simply to celebrate the church and the faith. However, the plague motif could sometimes play its role in their erection as well. Erecting religious monuments in the form of a column surmounted by a figure or a Christian symbol was a gesture of public faith that flourished in the Catholic countries of Europe especially in the 17th and 18th centuries. Thus they became one of the most visible features of Baroque architecture. This usage also influenced some Eastern Orthodox Baroque architecture.
Some other saints are also depicted on the plague columns. A typical one is St. Roch, who is said to have fallen ill when helping the sick during an epidemic of plague and who recovered through the strength of his faith. St. Sebastian, a martyr whose statue also often decorates these structures, was originally the patron of archers. In the Middle Ages Sebastian took the place of the plague-dealing archer Apollo, as people sometimes metaphorically compared the random nature of plague to random shots of archers, and thus he started being connected with the plague too. Other frequently depicted saints are St. Barbara, a patron of the dying, and two more recent and historical saints: St. Francis Xavier, who, according to the legend, raised people from the dead, and St. Charles Borromeo, known for working among the sick and the dying.
The Prague column was built in Old Town Square (Staroměstské náměstí) shortly after the Thirty Years' War in thanksgiving to the Virgin Mary Immaculate for helping in the fight with the Swedes. At noon its shadow indicated the so-called Prague Meridian, which was used to check the exact solar time. Many Czechs connected its placement and erection with the hegemony of the Habsburgs in their country, and after declaring the independence of Czechoslovakia in 1918 a crowd of people pulled this old monument down and destroyed it in an excess of revolutionary fervor.
The basic model which inspired building most Holy Trinity columns is the Pestsäule or Dreifaltigkeitssäule ("Plague or Holy Trinity column") in the Grabenplatz, Vienna, built after the 1679 plague; in this monument the column has entirely disappeared in marble clouds and colossal saints, angels and putti. The era of these religious structures culminated with the outstanding Holy Trinity Column in Upper Square (Horní náměstí) in Olomouc. This monument, built shortly after the plague which struck Moravia (nowadays in the Czech Republic) between 1714 and 1716, was exceptional because of its monumentality, rich decoration and unusual combination of sculptural material (stone and gilded copper). Its base was made so big that even a chapel was hidden inside. This column is the only one which has been individually inscribed on the UNESCOWorld Heritage List as "one of the most exceptional examples of the apogee of central European Baroque artistic expression".