Why Tapestry is Woven From the Bottom, Up

Lately, I've gotten some questions about whether one can weave tapestry from the top down rather than the bottom up. For some types of weaving I'm sure this works fine, but for tapestry weaving, starting at the bottom and weaving up is the best practice. 

Tapestry is architectural. It makes sense to build from the bottom up. In fact, it's tough to imagine building much of anything from the top down.

Why is that? Gravity. 

When you start weaving from the bottom up, building on each row below, your weft will get packed down evenly as more weft is layered over it. This creates a relatively dense and resilient piece. This resilience is one of the wonderful things about tapestries and the reason they last for a long time. When you weave from the top down, the weft threads are forced downward, making for wefts that are not densely as packed. 

Not all looms are positioned vertically like a Mirrix, of course, but even on a horizontal loom, it is much more difficult to pack your wefts upwards rather than downwards. 

Build up your weavings rather than building them down!