At the end of the 18th century and at the beginning of the 19th century the observatory buildings changed because the astronomical tools of observation changed from light portable equipment into permanently mounted accurate instruments. For positional astronomy, the observations were mainly carried out in the meridian or in the prime vertical. For observation of objects like planets, comets and double stars, a new type of telescope, the equatorially mounted refractor became important. The new instruments and methods of observation also required new approaches to observatory design. The outside appearance of the house, its whole structure from the foundations to the roof, and the functions of the observatory were determined by the new needs of science. At the beginning of the 19th century, new standards of observatory planning were developed when the new observatories of Tartu, Helsinki and Pulkovo were built. During many decades the principles adopted for their design guided the construction and architecture of avant-garde observatories round the world. They also provided for the archetype of the observatory as a universal emblem for science well into the 20th century. The steps of development of the design principles and their global impacts are discussed.