Clock Contemplations

If you didn't own a clock, and you lived before computers and phones,
how would you know when to start shabbos?

According to Wikipedia, rudimentary clocks like sundials and water
clocks existed in antiquity but these were neither precise nor
reliable. You would not, for example, be able to light your candles
precisely at 6:21 if all you had was a sundial. Mechanical clocks
didn't appear (again per Wikipedia) until the 12th century, but they
were very large and very expensive. Christians used them to signal
prayer times for entire towns. Did Jews have their own? I suppose so;
but did they exist in every Jewish community? At all times? Even
during periods of persecution? Hard to imagine.

I haven't made a study of this subject (as you can tell) but off the
top of my head, I see three possible solutions for the residents of
Jewish towns that didn't have centrally administered clocks.

1 - People relied on the sun, and (likely) often made mistakes and
started shabbos late.

2 - People relied on the sun, and (likely) often started shabbos
earlier than necessary. (No biggie)

3 - You followed the custom of an Egyptian community described by
Ovadya of Bartenura in his travel letters. They prayed mincha alone,
and then tucked into the first shabbos seuda when it was still light.
Later, after dark, they said maariv (this was before Kabalat Shabos
was invented.) I don't recall if R' Ovdya said if they went back to
shul for maariv or not; I suppose they didn't, because without watches
how would anyone know, in the dark, that it was time for the minyan?