This is the system I came up with to generate large family trees when I was running my Saxons! game, in which all the player characters were members of the same tribe.

It's not perfect, and it can be slow if you're just learning it (or making it up as was the case with me), but I think the end result is a fairly realistic method of building a family tree.

Key
+ marriage/mating
+x wife of dynasty member
+y husband of dynasty member
M male
F female
--- generational gap
[] profession
() dates of birth and death
/// notes to follow

Let's start with a founder, Sir Anselm. The Year is currently 500, we need to figure out his descendants.

First pick a starting date for your founder's birth. Then, to find their date of death, roll 3d20+20, which should give you an average expectancy of 50 years. In my case, I rolled a 7, so it would appear that dear Anselm expired too young at the age of 27. To spice things up, you can find a cause of death in the family history chapter appropriate of the year, or invent a cause of death to suit your fancy.

+ M Sir Anselm (410-437) [Vassal Knight, 1 Manor]

Next, let's give him a wife. To find the age difference between the two, roll 1d20-10, and add this figure to the husband's birth year. In this case I rolled a 1, so it would appear than Lady Catrin was 9 years Anselm's senior. Find her death date by the same method as the husband.

+ M Sir Anselm (410-437) [Vassal Knight, 1 Manor]
+x F Catrin (401-458)

Next, let's give them some children. We will only include the products of this union who lived to adulthood. We do not document the marriage date, only the date of the first child, working forward from the younger partner of the union. 1d6+20+birth for men, 2d6+13+birth for women. After the first child is found, we then work forward from there. Roll 1d6-1.

If the result is 0, roll again, adding the second roll. If the second roll is zero, the child is the fraternal twin of the previous child. Roll another d6, if the result is odd, the twins are identical.

If the result is 5, roll again and add the second result, ad ininitum if necessary.

Stop generation when the mother reaches the age of 40 or one of the parents dies.

+ M Sir Anselm (410-437) [Vassal Knight, 1 Manor]
+x F Catrin (401-458)
---------- M Child (431-476)
---------- F Child (432-488)

We'll call the boy Bryce. Let's throw the girl in a convent and call her Mary for convenience. Ordinary, one rolls 1d6 for every child, with a result of 6 or above resulting in holy orders, with a creeping +1 stacking modifier for every son or daughter after first.

+ M Sir Anselm (410-437) [Vassal Knight, 1 Manor]
+x F Catrin (401-458)
---------- M Bryce (431-476)
---------- F Mary (432-488) [*Nun*]

Following the same steps, we'll give Bryce a family.

+ M Sir Anselm (410-437) [Vassal Knight, 1 Manor]
+x F Catrin (401-458)
--------------------+ M Bryce (431-476) [Vassal Knight, 1 Manor]
--------------------+x F Helen (438-496)
---------------------------------------- M John (457-497) [Vassal Knight, 1 Manor]
---------------------------------------- M James (458)
---------------------------------------- F Gertrude (459-495)
---------------------------------------- M William (463)
---------------------------------------- F Isabelle (466) [*Nun*]
---------------------------------------- F Elizabeth (472)
-------------------- F Mary (432-488) [*Nun*]

And then finally, give those children families. Non landed, non priestly, sons have a 1 in 1d2 chance of starting a family.

+ M Sir Anselm (410-437) [Vassal Knight, 1 Manor]
+x F Catrin (401-458)
--------------------+ M Bryce (431-476) [Vassal Knight, 1 Manor]
--------------------+x F Helen (438-496)
----------------------------------------+ M John (457-497) [Vassal Knight, 1 Manor]
----------------------------------------+x F Adwen (461)
------------------------------------------------------------ F Joan (483)
------------------------------------------------------------ M Henry (485)
------------------------------------------------------------ M Richard (487)
------------------------------------------------------------ M Charles (488)
------------------------------------------------------------ F Catherine (491)
------------------------------------------------------------ F Anne (495)
---------------------------------------- M James (458) [Household Knight]
---------------------------------------- F Gertrude (459-495) +y John de Sutton Veny [Vassal Knight, 1 Manor]
---------------------------------------- M William (463) [Squire]
---------------------------------------- F Isabelle (466) [*Nun*]
---------------------------------------- F Elizabeth (472) +y Robert of Wilton [Merchant]
-------------------- F Mary (432-488) [*Nun*]

And there you have it.

There is probably a better way of doing this, but I haven't discovered one. I usually have this color-coded to gender and have living members bolded, but the BBCode is a bit wonk on this board, so I refrained in these examples.

Nice. :)

I have my own rolling system for the family, but I might swipe yours. In mine, I simply had a roll of the number of children (modified by the length of time from the marriage) and then a roll to see if the person was still alive or not at the campaign start (as in the rulebook). As I was focused more on the immediate family up to still-alive cousins, that was enough to come up with a reasonable family tree.

I do like the fact that you get the lifespan (although I am not totally convinced of 3d20+20, more of that later) and link the number of children to it, as well as having a chance of twins. I would have identical twins somewhat rarer (like on a roll of 6 on 1d6, rather than every odd number), although I am willing to admit that identical twins are a narrative trope in many stories (not that false Guinever was a twin, just a very very similar looking half-sister), and you already have only a 1/36 chance of twins. Also, I presume you roll for the gender of the twins first and only apply the identical twins if both are of the same gender? This would lower the chance of identical twins down to 1/144, which is low enough that it won't pop up often in the family tree anyway.

So, the 3d20+20... My main 'problem' with it is that the knights (and ladies) are almost guaranteed not to die young: Only 1% will die at 29 or younger. While I admit that this is very good for ensuring robust family trees, I would expect that a lot of the fighting is done by the younger knights, since they have the most to prove and need to make their fame and fortune. Also, the big killer of ladies would be childbirth, especially the first one, so again, one would expect that there would be somewhat higher mortality around the first decade of 'adulthood', when they are their most active in childbirth.

How to fix that? Well, I might apply something like a two-step method. First roll 1d6 to see at what the age category the person died in, and then roll the age accordingly:
1d6 Age at death
1-2 Died young: 1d20+20
3-5 Died middle aged: 1d20+40
6 Died old: 1d20+60

Rough calculation of the odds would give the expected lifespan to be something like (0.33*30.5 + 0.5*50.5 + 0.167*70.5) = about 47 years. But comparing how many people die in each category in my above system vs. your 3d20+20 (average 51.5)...
Died young: 33% in mine, 14% in yours (heavily weighted towards late 30s... comparing just the 20s, it is 16.7% vs. 1%)
Died middle-aged: 50% in mine, 66% in yours (almost symmetrical around 51.5, and pretty close to flat thanks to those 3d20s)
Died old: 16% in mine, 20% in yours (heavily weighted towards 60s, which I actually like better than my flat 1d20, but I am willing to accept that flatness rather than make a series of 1d6 rolls to address it)

So the big difference is that I have a much higher chance of people dying young. I gave my reasoning earlier why I want that, although I could add that there is also a population size at play. Using BotE death rates for adults (2.5% per year), you'll get something like 40% of the people dying between 20 and 40.

Very interesting.

I suggest a change in the roll for the spouse age difference. In most pre-industrialized countries men tend to marry women younger than themselves, even significantly (median woman age was 4-9 years younger in 1986). This is also true, albeit much downplayed, in industrialized countries (currently women are 2-3 years younger, as an average - probably corresponds to 1-2 years fot the median).
So, I suggest rolling 1d20-7 (or -6, or -8) for males, giving possible results in the -6 to +13 range.
In reality, extreme age differences are of course less frequent than moderate ones, so multiple die rolls would be better than a flat d20 to simulate this. A 4d6-10 roll generates a most frequent difference of +4 (11% chance, but 33% chance of +3 to +5), with possible results in the -6 to +14 range (about 1% chance for each extreme result).
For a higher chance of more couples with more balanced ages, increase the number of dice and decrease (less than proportionately) the subtracted number.

So, I suggest rolling 1d20-7 (or -6, or -8) for males, giving possible results in the -6 to +13 range.

Good point about the spousal age difference. In Pendragon, we'd expect that most vassal knights would marry as soon as they can (21). However, some can't afford to have a wife until they come to their inheritance, so they might be even older. At the same time, most women would marry young, in their late teens, to maximize their fertile years. The older women would likely be widows. Mr.47's rolling for the eldest child based on the age of the younger partner takes care of the problem of too young spouse nicely. I'd add +1 year to both, because even if they'd marry as young as reasonable (21 and 15), it will take almost a year for the baby to be born even if conceived on the wedding night. So minimum age of 22/16 would work better for me.

Good points all around, and duly adopted!

I've also forgotten I've got a set of rolls for recognized bastards.

First, to keep this from getting too ridiculous, determine if they're the kind of knight to A) go around fathering bastards, B) provide for said bastards, and C) acknowledge the existence and parentage of said bastards, at least passingly.. These three attributes are what's required to be mentioned on the family tree, in my book. So for every adult male who is not landed or a clergyman, roll 1d6, and if a 6 is rolled, the answer is yes. For landed males, roll 1d3, and proceed on a roll of 3.

Note that "fostered" and "recognized" bastards could mean an number of relationships ranging from "taken into the manor hall and treated the same as their siblings" and "the mother was given a cottage out in the woods and a bag of silver every time the father came by to 'visit' and had the children posthumously acknowledged".

One doesn't need to have land or property *yet* to father bastards, so theres nothing stopping the men on your family tree from popping them out in their teens, except for their own traits and the generosity of their family members.

Starting from age 16, determine bastards first. 1d20+15 for a pagan man's first fathered, recognized, and fostered bastard. 2d20+14 for christian men. On any roll of 20, roll an additonal 1d20-1 and add the result to the first.

If a bastard shows up, Make up their consort and add them to the tree with a +xC.

Roll 1d20 to determine class of the consort.

1-16 peasant
17-19 bourgeois
20 noble

Roll lifespan as you normally would for a wife, subtracting 10 years from a peasant consort and 5 years from a bourgeois consort. If the date of death is at or before the bastards date of birth, treat it as if the mother died in childbirth.

Wives are generally of the same age-group as the husband, even if the husband tends to be older. There is no such correlation with consorts. Find the age of the consort at the birth of the first bastard as 3d6+13.

From there, find subsequent children from that mother almost as you would for finding issue from a legitimate marriage, but with 2d6-2 between living issue, with twins occurring on a roll of 0.

Lastly, a man can have more than one consort after all. Roll 1d20-1 for the time it takes for the man to take another consort, after each of the following events:

a) death of consort
b) consort exceeds the age of 40



So, let's try this out, first with a Christian Knight who died in his 40's


+ M Laingren (400-44)
+xC F Viven (414-49) /// Peasant
-------------------- *I* M Laingren (440)
-------------------- *I* F Lengrina (442)
-------------------- *I* M Grenlain (445) /// Was conceived the night before his father rode to battle and died, born the following year.

Now, let's try the septuagenarian pagan knight.

+ M Lath (400-70)
+xC F Hollytte (404-54) /// Peasant
-------------------- *I* (428)
-------------------- *I* (433)
-------------------- *I* (441)
+xC F Lewysa (427-68) /// Peasant
-------------------- *I* (445)
-------------------- *I* (452)
-------------------- *I* (456)
-------------------- *I* (464)

And then let's throw this in to the family tree we had earlier.


+ M Sir Anselm (410-437) [Vassal Knight, 1 Manor] Christian
+x F Catrin (401-458)
--------------------+ M Bryce (431-476) [Vassal Knight, 1 Manor]
--------------------+x F Helen (438-496)
----------------------------------------+ M John (457-497) [Vassal Knight, 1 Manor]
----------------------------------------+x F Adwen (461)
------------------------------------------------------------ F Joan (483)
------------------------------------------------------------ M Henry (485)
------------------------------------------------------------ M Richard (487)
------------------------------------------------------------ M Charles (488)
------------------------------------------------------------ F Catherine (491)
------------------------------------------------------------ F Anne (495)
----------------------------------------+ M James (458) [Household Knight]
----------------------------------------+xC F Jeanne (461) /// Bourgeois, husband (mercer) ran off to the continent so unable to remarry
------------------------------------------------------------ *I* M Peter (487)
------------------------------------------------------------ *I* M Paul (496)
---------------------------------------- F Gertrude (459-495) +y John de Sutton Veny [Vassal Knight, 1 Manor]
---------------------------------------- M William (463) [Squire]
---------------------------------------- F Isabelle (466) [*Nun*]
---------------------------------------- F Elizabeth (472) +y Robert of Wilton [Merchant]
-------------------- F Mary (432-488) [*Nun*]
+xC F Fiona (417-432) /// Peasant, died in childbirth to fraternal twins.
--------------------+ *I* M Othor (432-460) [Steward]
--------------------+x F Julia (440-480)
---------------------------------------- F Fiona (456) +y Seamus MacTirnin [Gael Adventurer]
---------------------------------------- F Cornelia (457) +y Henry de Mayfield [Lord's Constable]
-------------------- *I* F Cordelia (432) +y Blain of Axe [Gentleman]



Bastards are of course strictly-speaking commoners, but they can be just a good source for squires and stewards and so on as any family member, for filling out household offices.