If you have a large amount of lines which you want to place a block on you can use the 'Line to Block' command. With this command you can select all the lines you wish to use. In the main menu of the command you can determine which geometry of the line should be considered. By default the command will use the midpoint of the line to place the block on. But you can also decide to use the end or startpoint of the line. A line can have it's start and endpoint on the same position so the line looks like a point. When they are not on the same position it means the line has a length. You can decide to base the scale of the new blocks on the length of the line it's placed on. So the longer the line, the bigger the block that will be placed. Besides a length two points also define an angle. You can choose to use that angle for the rotation of the block. With all these options you may the 'Line to Block' command an easy way to add blocks to your drawing.