He climbs to higher ground to  examine the shape of older burial structures that surrounded.

网友的质疑有道理。surround 通常是及物动词接宾语。根据意思，that 指structures，应该是这些 structures 环绕着他，在他周围。不应该是被动，被环绕。所以，原句应改为：

He climbs to higher ground to  examine the shape of older burial structures that surrounded him.