"There had been a monument before it was moved" is correct. We use the past perfect to show something that happened further in the past than another thing in the past (which takes the simple past tense). So if it is now 11:00, and A happened at 9:00 and B happened at 10:00, we'd use past perfect to discuss A and simple past to discuss B (e.g., "The light bulb had been on nonstop for 32 days before it burnt out.").