The Arab attack on Constantinople, 717 — From the Manasses Chronicle
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=20336270

Solidus of Leo III the Isaurian —
Photo Credit: By Classical Numismatic Group, Inc. http://www.cngcoins.com, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=25550509

Bronze statue of Constantine I — In York, England, near the spot where he was proclaimed emperor in 306
Photo Credit: By NewTestLeper79 - https://en.wikipedia.org/wiki/File:Constantine,_York_Minster.jpg, GFDL, https://commons.wikimedia.org/w/index.php?curid=38420825

Calleva Atrebatum plan —
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=1334305

Allectus on a coin —
Photo Credit: By Classical Numismatic Group, Inc. http://www.cngcoins.com, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=380124

Carausius on a gold aureus — Coin issued during the Carausian Revolt
Photo Credit: By Numismatica Ars Classica NAC AG - http://www.wildwinds.com/coins/ric/carausius/RIC_0005.jpg, CC BY-SA 3.0 ch, https://commons.wikimedia.org/w/index.php?curid=32942129

Council of Nicaea 325 — Fresco in Capella Sistina, Vatican
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=30734368

Constantine the Great summoned the bishops — Constantine the Great summoned the bishops of the Christian Church to Nicaea to address divisions in the Church (mosaic in Hagia Sophia, Constantinople (Istanbul), ca. 1000).
Photo Credit: By Byzantine mosaicist, ca. 1000 - Public Domain, https://commons.wikimedia.org/w/index.php?curid=148609

Arius —
Photo Credit: By Unknown - Public Domain, https://commons.wikimedia.org/w/index.php?curid=15860779

Icon of the Pope Alexander of Alexandria — In Veljusa Monastery
Photo Credit: By Unknown author - http://www.ii.edu.mk/predmeti/mm/20052006/mmproekti/Strumica/Veljusa/VeljusaFreski.html, FAL, https://commons.wikimedia.org/w/index.php?curid=7903378

Helena's sarcophagus — In the Museo Pio-Clementino, Vatican Museums, Rome
Photo Credit: By Joshua Sherurcij, Attribution, https://commons.wikimedia.org/w/index.php?curid=3872281