Complex sentence: The castle at the north with polygonal masonry was built in the second century BC. Its dimensions are 105 x 60 m 2, but only the tower at the east wall is standing.
Split into simpler sentences: The castle at the north with poygonal wall stones, had been built in the second century BC. Its dimensions are 105 x 60 m 2. But only the tower at the east wall is standing.