These strange structures were built by both Deitech and its predecessors in the United Republic Of Mercaulis (and other locations) between 2257 PC and 2379 PC.
Additional structures may have been built by others, but there is little hard evidence of this.
The official name for these structures within the Northern Bloc government is Liminal Construct or LiCon.
The Isylorian Order refers to them as a Thyriatic Edifice.
These are the technological zenith of the 4th era of humankind.