Very badly decayed and extremely poor. This is before the Frangipani family, and others, pooled their commercial resources to rebuild the wealth of Rome and restart monumental construction. The earthquake of 847 south in the Apennine mountains probably also did damage to Rome, and perhaps as well the 846 Arab raid on Rome outside the walls.

By 1000, the old forums were used for pasture and enclosures for animals and had already been for centuries. Ancient monuments had become quarries for building materials. Only those buildings repurposed for the church or fortifications were saved. Some of the prominent buildings were relatively intact still, e.g. the bulk of the Colosseum, Basilica of Maxentius, and baths still stood, we think, until the earthquake of 1349.

There would have been very low population density, although at 30,000 Rome still would have been a major city by the standards of the early-high Middle Ages. We tend to forget that, when talking about the depths to which Rome sank, Paris and London had even fewer people at this time.

I do not know who owns the copyright to these, but this is how I imagine Rome in 1000 CE.

Forum of Nerva

Curia Julia/Forum of Caesar in the foreground/Arch of Septimius Severus and Forum Romanum behind the Curia

Left to right: Basilica Ulpia, Forums of Trajan (with the market in back), Augustus, Nerva, Caesar (front/left), Curia intact at the bottom, Temple of Peace all the way to the right.

And what they used to look like …