Wikipedia
Zalesye (; literally: "area beyond the forest") or Opolye (Опо́лье; literally: "area in the fields") is a historical region of Russia, comprising the north and west parts of Vladimir Oblast, the north-east of Moscow Oblast and the south of Yaroslavl Oblast. As a kernel of the medieval state of Vladimir-Suzdal, this area played a vital part in the development of Russian statehood.
The name alludes to the deep woods that used to separate the medieval Principality of Rostov from the Republic of Novgorod and the Dnieper principalities. Before the coming of Slavs in the 9th century, the area was inhabited by Merians, Muroma, and other Finnic tribes. In the 10–12th centuries these tribes were subsequently assimilated by the Slavic settlers.
In the twelfth century, this fertile area, being well protected from Turkic incursions by the forests, provided a favourable oasis for Slavic people migrating from the southern borders of Kievan Rus. The population of the area rapidly increased and by 1124 reached the point when Yuri Dolgoruki found it expedient to move his princely seat from Rostov in the Upper Volga Region to Suzdal in Zalesye.
Suzdal was the oldest and most senior town of Opolye. Other important urban centres were established by Yuri in Pereslavl-Zalessky (founded 1152), Yuriev-Polsky (1152), Dmitrov (1154), Starodub-on-the-Klyazma (1152), Vladimir-Zalessky (1108), Ksnyatin (1136), and Yaropolch-Zalessky (1136). The monikers Zalessky ("over the woods") and Polsky ("in the fields") were used to distinguish new cities from the eponymous towns now in modern-day Ukraine.
Being perpetually at odds with the powerful Suzdalian boyardom, Yuri even contemplated moving his capital from Suzdal to the new town of Pereslavl-Zalessky. His unexpected death led to the idea being dropped, but Yuri's son Andrew the Pious finally moved the princely seat to another young town, Vladimir. The old nobility of Rostov and Suzdal, however, arranged Andrew's assassination and a brief civil war for supremacy in Zalesye followed.
During the Mongol invasion of Russia, when the woods were gradually being cleared and new centres developed in Moscow, Tver, and elsewhere, the strategic importance of Zalesye declined. New urban centres were developed around famous monasteries (e.g., Sergiev Posad, Kirzhach) or royal residences (e.g., Alexandrov, Radonezh).
Sometimes, the term Zalesye is taken to include the whole Upper Volga and Lower Klyazma region. In this sense, Zalesye is equivalent with the territory included within the Golden Ring of Russia.