From this excellent book:
The brutal truth is that architecture is too important to be left exclusively to a few people. It’s fine to have an architect, but the key way to keep an architecture intact is to make sure that everyone on the team knows what it is and has a stake in it. Every person who is touching the code should know the architecture, and everyone else who touches the code should be able to benefit from what that person has learned. When everyone is working off of the same set of ideas, the overall system intelligence of the team is amplified. If you have, say, a team of 20 and only 3 people know the architecture in detail, either those 3 have to do a lot to keep the other 17 people on track or the other 17 people just make mistakes caused by unfamiliarity with the big picture.