Unless you have one hell of a wide rim built into the hole, the diagonal will normally be easily long enough to allow the cover to fall in if it's not place just right. Round - no possibility of this.

>This is a perfect example of why the question is silly and
>reveals nothing about the person you asked it to.
>
>Square or triangular manhole covers would not fall into their
>holes either (assuming they are placed correctly) because the rim
>of the hole supports the cover. This is not a function of the cover,
>its a function of the overall design.
>
>My line of thinking when I saw the question was:
>
>1) What in the world does this have to do with the position?
>2) Who cares?
>3) This guy has nothing better to ask me that why a manhole cover is round?
>4) I have more important things to do with my time than entertain silly questions
>5) I'm outta here
>
>
>
>
>
>
>
>>>So, why are manhole covers round?
>>
>>To prevent the manhole cover from falling into the manhole.
>>
>>Einar
>>>
>>>
>>>
>>>>Kevin,
>>>>If you interviewed someone and asked them: "Why are manhole covers round?" and they answered: "What does any of this have to do with weather or not I can write solid code? Don't ask me silly questions! Ask me a relevant question!". Would you hire that person?
>>>>
>>>>Hey "crazy" questions works for M$. I am sure they have put some thought into it :)
>>>>
>>>>Einar
>>>>
>>>>>What does any of this have to do with weather or not someone
>>>>>can write solid code?
>>>>>
>>>>>I have no idea which way to look to find Venus. I'v been writing
>>>>>successfull applications for 20 years.
>>>>>
>>>>>
>>>>>
>>>>>>>Isn't an IQ question a "logic question"? lol
>>>>>>>I see your point though.
>>>>>>>Einar
>>>>>>
>>>>>>
>>>>>>Maybe some knowledge Q's?
>>>>>>
>>>>>>- Why are manhole covers round?
>>>>>>- What's a prime number? (definition of)
>>>>>>- If you wanted to find Venus on the sky, which way would you look towards?