Complex sentence: The forum had a rectangular plan 250 x 300, and its shape was still recognizable in the fifties of 20th century as an empty space limited to the north by 7-8 meters high terraces.
Split into simpler sentences: The forum had a rectangular plan 250 x 300. In the fifties of 20th century its shape was still recognizable as an empty space limited to the north by 7-8 meters high terraces.