Complex sentence: During the partition of his father's lands, he received the town of Yuriev-Polsky, where he built its chief landmark, the Cathedral of St. George, in 1230-34.
Split into simpler sentences: During the partition of his father's lands, he received the town of Yuriev-Polsky. It was he who commissioned the town's principal landmark, the Cathedral of St. George, constructed in 1230-34.