(Collecta: S. Adrian)
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From Blessed Ildefonso Schuster's The Sacramentary:
The church of the deaconry of St. Adrian is in the Forum in the former aula of the Senate. It was dedicated by Pope Honorius I (625-38) to the memory of this famous martyr of Nicodemia, who, during the Byzantine era, was the object of much devotion in Rome, where churches and monasteries were built in his honour.
The stational basilica de Pallacine, dedicated later on to St. Mark the Evangelist, was erected by the Pope of that name (337-40), and is the only church in Rome sacred to the memory of this devoted disciple... Under the high altar of the titulus Marci rests the body of the founder with the relics of the martyrs of Abdon and Sennen.
From the Churches of Rome wiki:
The basilica was probably founded by Pope St Marcus (Mark) in 336, and is one of Rome's oldest churches. It stand on the site where St Marcus is said to have lived, and was known as the Titulus Pallacinae.
The church was rebuilt in the 5th century, and was left facing the opposite direction.
It was reconstructed in the 8th century by Pope Adrian I (772-795), and given back its original orientation, which it has today. It was flooded when the Tiber rose above its banks soon after, in 791. Pope Gregory IV (827-844) restored it after the flood.
Pietro Cardinal Barbo, titular of the church and later Pope Paul II, restored it again in 1455-1471. At the same time, he built the Palazzo Venezia. Cardinal Barbo declared San Marco as the national church of the Venetians.
In 1744, it was changed into a baroque church by Filippo Barigioni.
[...]
The apse mosaic dates from the 9th century, and was ordered by Pope St Gregory IV (827-844)... Christ is standing in the middle, flanked by the St Felicissimus, St Mark the Evangelist, Pope Gregory IV on the left and Sts Pope Marcus, Pope Agapitus and Agnes on the right. St Mark has his hand on Pope Gregory's shoulder, meaning that he is introducing him to Christ.
