acitus wrote a treatise on the German people titled Germania which, despite its biases, provides useful information about the Germans including the Goths. Selected quotes below:
The people of Germany appear to me indigenous, and free from intermixture with foreigners, either as settlers or casual visitants. For the emigrants of former ages performed their expeditions not by land, but by water; and that immense, and, if I may so call it, hostile ocean, is rarely navigated by ships from our world. Then, besides the danger of a boisterous and unknown sea, who would relinquish Asia, Africa, or Italy, for Germany, a land rude in its surface, rigorous in its climate, cheerless to every beholder and cultivator, except a native?