The Hill of Crosses is a site of pilgrimage in northern Lithuania. The precise origin of the practice of leaving crosses on the hill is uncertain, but it is believed that the first crosses were placed on the former Jurgaičiai or Domantai hill fort after the 1831 Uprising. Over the centuries, not only crosses, but giant crucifixes, carvings of Lithuanian patriots, statues of the Virgin Mary and thousands of tiny effigies and rosaries have been brought here by Catholic pilgrims. The number of crosses is unknown, but estimates put it at about 55,000 in 1990 and 100,000 in 2006.
In 1795, Lithuania became part of the Russian Empire. Poles and Lithuanians unsuccessfully rebelled against Russian authorities. These uprisings are connected with the beginnings of the hill: as families could not locate bodies of perished rebels, they started putting up symbolic crosses in place of a former hill fort.
When the old political structure of Eastern Europe fell apart in 1918, Lithuania once again declared its independence. Throughout this time, the Hill of Crosses was used as a place for Lithuanians to pray for peace, for their country, and for the loved ones they had lost during the Wars of Independence.
Most recently, the site took on a special significance during the years 1944–1990, when Lithuania was occupied by the Soviet Union. Continuing to travel to the Hill and leave their tributes, Lithuanians used it to demonstrate their allegiance to their original identity, religion and heritage. It was a venue of peaceful resistance, although the Soviets worked hard to remove new crosses, and bulldozed the site at least three times (including attempts in 1963 and 1973).
Today the hill remains under nobody's jurisdiction; therefore people are free to build crosses as they see fit.
From: http://en.wikipedia.org/wiki/Hill_of_Crosses