The Tower by Valerio Massimo Manfredi

AD 70. A ferocious, mysterious force hidden in a solitary tower annihilated a squad of Roman soldiers advancing through the Sahara desert. There was a single the Etruscan diviner Avile Vipinas, who later described the horror of the creature in the tower and suggested how it could be destroyed. Nearly 2,000 years later, to find the tower and solve its unutterable mystery, three men venture into the heart of the an archaeologist following the traces of his father, a colonel from the Foreign Legion thirsting for revenge, and a priest who puts his faith to the ultimate test. Just what is the dark being that slumbers in the tower?