The reason being that so little was known about undergarments worn in those days. The bra and knickers shown were found in an Austrian castle. Here's an excerpt from the article which accompanied the pics
"Lengberg Castle, first documented in 1190, was rebuilt into a representative palais in the 15th century by adding a second floor. During extensive reconstruction in July 2008, a vault filled with waste was found beneath the floorboards of a room on the second storey of the castle, where it was dumped during the 15th-century reconstruction.
Due to dry conditions in the vault the organic waste, mainly consisting of worked wood, leather (shoes) and textiles had been extremely well preserved, and four of the linen fragments resemble modern bras. The criterion is the presence of distinct cut cups – in contrast to antique Greek or Roman breast bands, simple strips of cloth or leather wound around the breasts and designed to flatten rather than enhance.
There are some written
medieval sources on possible female breast support, but they are rather vague on the topic. Henri de Mondeville, surgeon to Philip the Fair of France and his successor Louis X, wrote in his
Cyrurgia in 1312–20: “Some women… insert two bags in their dresses, adjusted to the breasts, fitting tight, and they put them [the breasts] into them [the bags] every morning and fasten them when possible with a matching band.”
These ‘bags’ served the same purpose as antique breast bands – that is to contain two large breasts. However, the “shirts with bags in which they put their breasts” that Konrad Stolle complained about in his chronicle of Thuringia and Erfurt in 1480 seem to have obtained the opposite effect, as he concludes his description with the words “all indecent”.
An unknown 15th-century author of southern Germany was definitely referring to breast-enhancement in his satirical poem as he wrote: “Many [a woman] makes two breastbags [bags for the breasts], with them she roams the streets, so that all the young men that look at her, can see her beautiful breasts; But whose breasts are too large, makes tight pouches, so there is no gossip in the city about her big breasts.” As we can see, medieval bras worked both ways."
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