There are no certificates of birth for most of my ancestry, that is a XX century thing.  I using the paroquial registries, they have the births and marriages. So I'm going backwards from marriage -&gt; birth. In the paroquial books the marriage regist says the age of the person and where he's from (besides the profession), so you use that info to see the birth regist and find out who their fathers were. Then repeat :p But you got to physically go to the registries in every parroquia in Portugal or is there an online database with the info? Maybe I'm asking too much :D