Meanings of cruciform structure in английском

I look up and see that the cruciform structure is empty, whatever that means.

This is a fine cruciform structure, with a central tower and a quite remarkable W. front.

At present the cathedral is a regular cruciform structure of Norman character, remarkable for the solidity of its construction.

It is a large cruciform structure with a central tower, having three windows in the belfry, and rather shallow buttresses.

The fine cruciform structure, with a handsome four storied central tower, dates from about 1420 and occupies the site of an older building, probably Norman.