To preface this question, I will say that I work at a Sewage Treatment Plant. I work in an office, not in the field, and honestly, it is the GREATEST job I've ever had. I love my co-workers, and I can tell you more about sewage treatment and our sewer system than most people. It is a very interesting job.
My husband on the other hand is a Computer Software Developer. Years ago Microsoft began asking the question "Why are manholes round?" during their interview process. That has in turn caused my husband's developer friends to ask the same question of me when they find out I work in the Sewer Department.
So, to any of you planning to interview at Microsoft, there are a few different answers to the question, but the answer that is mostly the right one is that manhole covers are round so that the cover can't fall into the hole. Other acceptable answers would be because humans can easily access the manhole do to our "round" mid sections, and since the weight of a cover is around 100lbs (or larger) the round shape makes it easier to roll the cover away from the manhole during maintenance.
This has nothing to do with Fostering, but I felt the need to blog something. I'm getting a bit agitated that I turned down two placements while on vacation, and now my phone isn't ringing at all. I guess it will happen soon enough!