It means the 1st-born! From 'A' - the alphabetic sign for No.1 until the introduction of Latin numerals and later Indo-Arabic; and Latin 'nātālis' (“natal”), from 'nātus', perfect active participle of 'nāscor' (“I am born”), ultimately from Proto-Indo-European *ǵenh₁- (gene), related to Macedonic "Žena" - woman and/or Sanskrit 'Janani' - mother, actually the very one that gives a birth to the 'Firstborn' i.e. Anatolius.
Frans Anatolius Sjöström (1840 – 1885) was a Finland Swedish architect. He was born in Turku and educated there and, in 1868, at the Royal Swedish Academy of Arts. In 1872 he designed the old building of the Helsinki University of Technology.