Wikipedia
Dziady, an ancient Slavic feast, commemorated the dead. Literally, the word translates as "Grandfathers".
The commemoration took place twice every year (in spring and in autumn). During the feast the ancient Slavs organized libations and ritual meals. In local mythologies such feasts were organized both for the living and for the souls of the forefathers who joined the dziady after dark.
In Poland the tradition survived in the form of Christian Zaduszki feast.
In Belarus, Dziady (Дзяды) usually took place on the last Saturday before St. Dmitry's day, at the end of October/beginning of November (Dźmitreuskija dziady, St.Dmitry's Dziady). There were also ' Trinity Day Dziady', ' Shrovetide Dziady', and some other dates.
Lithuanians have similar feast day, called Ilgės. It has roots in pagan times, and differs slightly from the Slavic Dziady.
In 1988 the newly-founded Belarusian Popular Front (BPF) initiated the revival of the tradition in Belarus. In addition, on this day a rally to Kurapaty on the outskirts of Minsk is arranged, in the memory of the victims of Soviet political repressions. The communist administration of the country at that time strongly opposed the initiative. The BPF and other movements in Belarus have continued the tradition.
Much of the second part of Adam Mickiewicz's verse drama Dziady (published in 1823) depicts the Dziady feast organized in what is now Belarus, and popular among Ruthenians and Lithuanians during the times of the Polish-Lithuanian Commonwealth.
Dziady (, Forefathers' Eve) is a poetic drama by the Polish poet Adam Mickiewicz. It is considered one of the great works of European Romanticism. To George Sand and Georg Brandes, Dziady was a supreme realization of Romantic drama theory, to be ranked with such works as Goethe's Faust and Byron's Manfred.
The drama's title refers to Dziady, an ancient Slavic and Lithuanian feast commemorating the dead (the "forefathers"). The drama comprises four parts, the first of which was never finished. Parts I, II and IV were influenced by Gothic fiction and Byron's poetry. Part III joins historiosophical and individual visions of pain and annexation, especially under the 18th-century partitions of Poland. Part III was written ten years after the others and differs greatly from them. The first to have been composed is "Dziady, Part II," dedicated chiefly to the Dziady Slavic feast of commemoration of the dead which laid the foundations of the poem and is celebrated in what is now Belarus.
A ban on the performance of the play was an aspect of the 1968 Polish political crisis.