Merging vertices

Support Modeling
1

Hi Guys

Am learning Blender and I just made a tutorial about an medieval Arch. I have made one and duplicate it three time. As you can see in the screenshot, all the selected vertices needs to be merged to finalise the mesh. The only way I know is to merge them one by one, selecting two vertices and then merge them together then the same with the nest two. etc. I was wondering if there was a way to merge them using one command.
http://misc.cgcookie.netdna-cdn.com//pencil.png

2

Select all the vertices (A) and W / Remove Doubles. Either at the bottom of the toolshelf (T) or by F6 you can then adjust the Merge Threshold if the vertices are not exactly in the same location.

3

Thank you sir, that worked