What is "lilanje"

Lilanje ( Serbian cyrilic:лилање Serbian pronounce:lilaɲe) is the religious Serbian national custom when dry birch or cherry cortex placed on the wooden stick named Lila, olalija, oratnik or oratnica is burned. Lilanje is celebrated the night before St John's Eve, Feast of Saints Peter and Paul, Feast of the Ascension and Ilindan. It is most connected to 'Petrovdan', the Serbian Slava of St. Peter. Some people think the name olalija comes from the Roman word for the Roman custom Parilia. Mostly just young people are celebrating Lilanje. It is celebrated on the big places like squares where the big fire is placed. This custom is older than Christianity. It has appeared because people thought that in the night fire scares demons and witches and protects people, animals and fields.