During his residence in the Persian capital, he made the acquaintance of Pietro della Valle, a Roman gentleman of considerable fortune, who had been travelling for some years in the East. In consequence of a disappointment in love he had sought relief in foreign adventure, and at the age of twenty-nine he embarked at Venice for Constantinople. After visiting Egypt and the Holy Land, he crossed the desert to Bagdad. At that time Bagdad was commonly supposed to be built on the site of the ancient city of Babylon. But Della Valle had no difficulty in pointing out that this was evidently an error, for we know that the one city was built on the Tigris, while the other stood on the Euphrates. He made several excursions through Mesopotamia, and visited the mounds near Hillah, which he had no doubt covered the ruins of the true Babylon. He has left an account of the state in which he found them, which may still be read with interest; and he picked up some of the bricks, both baked and unbaked, of which they are composed.[20] These he subsequently brought back with him to Rome, where they were included in his private collection of antiquities. They were perhaps the first specimens that ever reached Europe, and a few of them may still be seen in the Museo Kircheriano. He indulged his antiquarian tastes by endeavouring to ascertain the sites of some of the famous cities of antiquity, and he seems to have been the first to identify that of Ctesiphon correctly. At Bagdad he married a Mesopotamian lady, and afterwards crossed the mountains of Kurdistan into Persia. He was cordially welcomed to the Court by Shah Abbas, who enrolled him among the privileged number of ‘Guests of the King.’