Born the son of a teacher, Carl Rathjens began his academic studies in 1906 in the University of Hamburg, and then continued to expand his higher education in the universities of Kiel, Berlin and Munich on the subjects of geography, geology, cartography, meteorology, astronomy, botany, zoology, demography, sociology and economy.

Rathjens travelled to Egypt as a young German student of geography, geology, astronomy, meteorology and biology.

At short notice, and without planning, he continued on his journey and traveled to Ethiopia in 1908, accepting a friend's proposal to visit his uncle who officiated there as a priest.

In 1911 he earned his doctorate under Erich von Drygalski with the thesis, Beiträge zur Landeskunde von Abessininen ("Contributions to the Geography of Abyssinia"), in which he proposed to his professor the writing of a follow-up thesis for a habilitation degree, entitled, Die Juden in Abessinien, which would permit him to instruct as a professor.

Upon their arrival in Hodeida, Carl Rathjens wrote to his family in Hamburg that when he entered Yemen he had “left civilization behind him; there are no banks, neither hotels, nor embassies.

Already on his first visit, he developed a good rapport with the king, the Imām Yaḥyā Ḥamīd ad-Dīn (1864-1948) and his five elder sons, all of whom were serving the country and had ministerial posts, or else managed an important position in the court.

In his letters to family members and friends, he had repeatedly described how he enjoyed the hospitality of the king and felt that his life in Sana'a was like a chapter taken from the book, A Thousand and One Nights.

This gave him the incentive to request from Imam Yahya that he establish a Ministry of Antiquities and to build a museum in which the archaeological findings could be stored and preserved.

Rathjens also suggested that the Imam should invite from Germany a team consisting of an archaeologist and philologist for ancient Semitic languages in order to inspect the excavations, as well as to document their findings and do the deciphering of the inscriptions, by using strict scientific methods as those used in Europe.

Rathjens was astonished that no public inspection had been put in place to make the trade in antiquities contraband on the markets of Sana'a, Taiz, Hodeida, Amram, Dhamar and Saada.

Furthermore, he was also witness to conversations with foreign traders and tourists who ordered certain items from a certain region, by which means they encouraged the locals to dig-up and rob ancient graves and treasures and to clandestinely bring their findings for sale in the marketplaces.

Rathjens started by drawing a plan of the building, but he himself had to look for wood in the remote outlying districts of Sanaa and to bring the material into the capital.

The Wetter Dienst (“weather service”) station in Hamburg donated many measuring instruments and which Rathjens brought to Yemen.

Such data had already been collected in the past by a previous scholar, Carsten Niebuhr, who in 1763 measured the effects of temperature and precipitation during his first few weeks in Yemen.

Eduard Glaser, who had spent more time in Sana’a and had made numerous visits to Yemen at the end of the 19th century, also brought from Germany instruments to measure the temperature, the humidity and the precipitation.

The Imam instructed the director-general of the post office of Sana’a to assist him in these endeavors, while Rathjens went to Berlin to order new stamps that would also be recognized outside of Yemen.

After finishing the preliminary preparations for the newer post office, Rathjens submitted an application for Yemen under the Imam to become a member of the International Postal and Telegraph Association.

He was also very interested in Rathjens working for him as a consultant for buying weapons in Europe, as well as other industrial commodities to help in the modernization of his country.

Rathjens was also very interested in Germany developing friendly relations with Yemen and that the two countries would expand their commercial exchanges.

In Yemen, Rathjens studied the political and juridical system of the courtiers, including the demographic structure of the nation, and informed his readers about minority groups living in the country, their social and legal status.

[4][5] Carl Rathjens was avant-garde in systematically processing the flora of South Arabia, which he saw there in 1927 and 1928, and added considerably to knowledge in this field.

Most of the collectable items which he brought out of Yemen are today stored in the Museum of Ethnology in Hamburg (Museum für Völkerkunde Hamburg), among which are hundreds of inscriptions from the Himyaritic and early Islamic period, Arabic and Hebrew manuscripts, thousands of items relating to ethnography and the documentation of the material culture in Yemen.

In 1939, Salman Schocken (1877–1959) purchased some 800 objects from Rathjens' collection of Yemenite Jewry's ethnographic material, which he then loaned to the Bezalel Museum at the insistence of Erich Brauer and Hadasah Perlman-Ḳalṿari-Rozenbliṭ.