Can a Building permit expire?

[maud gonne]

I'm wondering, how do 'they" know if 120 days have passed without the work commencing. Does anyone come out and check? I can foresee my not getting all my ducks in a row in time but I'd hate to have to reapply and repay for a permit when I'm making every effort to "commence." And I also wonder whether clearing and installing a septic system would count as commencing the work based on a building permit...